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 $167.68   9.319%   $183.3061   $183.31   $183.30   $183.30  
  Purchase #2 $244.52   8.346%   $264.9276   $264.93   $264.95   $264.90  
  Purchase #3 $150.96   12.457%   $169.7651   $169.77   $169.75   $169.80  
  Purchase #4 $50.86   3.228%   $52.5018   $52.50   $52.50   $52.50  
  Purchase #5 $182.44   6.828%   $194.897   $194.90   $194.90   $194.90  
  Purchase #6 $6.26   11.342%   $6.97   $6.97   $6.95   $7.00  
  Purchase #7 $7.89   3.500%   $8.1662   $8.17   $8.15   $8.20  
  7 purchase totals = $810.61       $880.5338   $880.55   $880.50   $880.60