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 $59.49   8.819%   $64.7364   $64.74   $64.75   $64.70  
  Purchase #2 $101.76   11.244%   $113.2019   $113.20   $113.20   $113.20  
  Purchase #3 $124.74   3.769%   $129.4415   $129.44   $129.45   $129.40  
  Purchase #4 $116.81   7.674%   $125.774   $125.77   $125.75   $125.80  
  Purchase #5 $103.46   12.629%   $116.526   $116.53   $116.55   $116.50  
  Purchase #6 $227.62   6.476%   $242.3607   $242.36   $242.35   $242.40  
  Purchase #7 $152.29   11.353%   $169.5795   $169.58   $169.60   $169.60  
  7 purchase totals = $886.17       $961.6200   $961.62   $961.65   $961.60