Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $214.53   8.283%   $232.2995   $232.30   $232.30   $232.30  
  Purchase #2 $141.31   12.655%   $159.1928   $159.19   $159.20   $159.20  
  Purchase #3 $158.80   6.654%   $169.3666   $169.37   $169.35   $169.40  
  Purchase #4 $210.95   11.118%   $234.4034   $234.40   $234.40   $234.40  
  Purchase #5 $141.95   11.329%   $158.0315   $158.03   $158.05   $158.00  
  Purchase #6 $145.44   5.821%   $153.9061   $153.91   $153.90   $153.90  
  Purchase #7 $232.62   8.418%   $252.202   $252.20   $252.20   $252.20  
  7 purchase totals = $1,245.60       $1,359.4019   $1,359.40   $1,359.40   $1,359.40