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 $76.41   10.674%   $84.566   $84.57   $84.55   $84.60  
  Purchase #2 $145.54   9.595%   $159.5046   $159.50   $159.50   $159.50  
  Purchase #3 $116.62   9.557%   $127.7654   $127.77   $127.75   $127.80  
  Purchase #4 $35.58   4.449%   $37.163   $37.16   $37.15   $37.20  
  Purchase #5 $189.64   4.263%   $197.7244   $197.72   $197.70   $197.70  
  Purchase #6 $17.67   5.304%   $18.6072   $18.61   $18.60   $18.60  
  Purchase #7 $157.35   7.388%   $168.975   $168.98   $169.00   $169.00  
  7 purchase totals = $738.81       $794.3056   $794.31   $794.25   $794.40