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 $60.78   6.520%   $64.7429   $64.74   $64.75   $64.70  
  Purchase #2 $158.90   6.412%   $169.0887   $169.09   $169.10   $169.10  
  Purchase #3 $248.30   6.733%   $265.018   $265.02   $265.00   $265.00  
  Purchase #4 $198.97   9.828%   $218.5248   $218.52   $218.50   $218.50  
  Purchase #5 $72.74   8.618%   $79.0087   $79.01   $79.00   $79.00  
  Purchase #6 $193.97   3.392%   $200.5495   $200.55   $200.55   $200.50  
  Purchase #7 $68.30   10.544%   $75.5016   $75.50   $75.50   $75.50  
  7 purchase totals = $1,001.96       $1,072.4342   $1,072.43   $1,072.40   $1,072.30