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 $195.93   4.677%   $205.0936   $205.09   $205.10   $205.10  
  Purchase #2 $150.93   12.339%   $169.5533   $169.55   $169.55   $169.60  
  Purchase #3 $84.38   3.313%   $87.1755   $87.18   $87.20   $87.20  
  Purchase #4 $25.83   4.495%   $26.9911   $26.99   $27.00   $27.00  
  Purchase #5 $67.76   7.158%   $72.6103   $72.61   $72.60   $72.60  
  Purchase #6 $110.28   5.729%   $116.5979   $116.60   $116.60   $116.60  
  Purchase #7 $72.51   12.397%   $81.4991   $81.50   $81.50   $81.50  
  7 purchase totals = $707.62       $759.5208   $759.52   $759.55   $759.60