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 $60.30   11.674%   $67.3394   $67.34   $67.35   $67.30  
  Purchase #2 $169.66   6.371%   $180.469   $180.47   $180.45   $180.50  
  Purchase #3 $152.40   6.225%   $161.8869   $161.89   $161.90   $161.90  
  Purchase #4 $210.48   9.151%   $229.741   $229.74   $229.75   $229.70  
  Purchase #5 $117.57   7.130%   $125.9527   $125.95   $125.95   $126.00  
  Purchase #6 $104.96   10.761%   $116.2547   $116.25   $116.25   $116.30  
  Purchase #7 $173.92   12.190%   $195.1208   $195.12   $195.10   $195.10  
  7 purchase totals = $989.29       $1,076.7645   $1,076.76   $1,076.75   $1,076.80