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 $210.81   11.144%   $234.3027   $234.30   $234.30   $234.30  
  Purchase #2 $163.62   10.700%   $181.1273   $181.13   $181.15   $181.10  
  Purchase #3 $89.89   7.426%   $96.5652   $96.57   $96.55   $96.60  
  Purchase #4 $98.82   9.123%   $107.8353   $107.84   $107.85   $107.80  
  Purchase #5 $154.28   3.749%   $160.064   $160.06   $160.05   $160.10  
  Purchase #6 $223.66   11.265%   $248.8553   $248.86   $248.85   $248.90  
  Purchase #7 $153.84   10.565%   $170.0932   $170.09   $170.10   $170.10  
  7 purchase totals = $1,094.92       $1,198.8430   $1,198.85   $1,198.85   $1,198.90