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 $37.64   4.633%   $39.3839   $39.38   $39.40   $39.40  
  Purchase #2 $155.25   4.485%   $162.213   $162.21   $162.20   $162.20  
  Purchase #3 $37.80   9.380%   $41.3456   $41.35   $41.35   $41.30  
  Purchase #4 $150.53   9.227%   $164.4194   $164.42   $164.40   $164.40  
  Purchase #5 $228.99   6.434%   $243.7232   $243.72   $243.70   $243.70  
  Purchase #6 $116.95   4.134%   $121.7847   $121.78   $121.80   $121.80  
  Purchase #7 $169.59   12.830%   $191.3484   $191.35   $191.35   $191.30  
  7 purchase totals = $896.75       $964.2182   $964.21   $964.20   $964.10