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 $58.84   11.571%   $65.6484   $65.65   $65.65   $65.60  
  Purchase #2 $223.62   6.713%   $238.6316   $238.63   $238.65   $238.60  
  Purchase #3 $69.47   9.220%   $75.8751   $75.88   $75.90   $75.90  
  Purchase #4 $185.91   5.384%   $195.9194   $195.92   $195.90   $195.90  
  Purchase #5 $44.83   12.458%   $50.4149   $50.41   $50.40   $50.40  
  Purchase #6 $5.65   11.531%   $6.3015   $6.30   $6.30   $6.30  
  Purchase #7 $184.36   10.274%   $203.3011   $203.30   $203.30   $203.30  
  7 purchase totals = $772.68       $836.0920   $836.09   $836.10   $836.00