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 $153.98   8.308%   $166.7727   $166.77   $166.75   $166.80  
  Purchase #2 $228.56   10.213%   $251.9028   $251.90   $251.90   $251.90  
  Purchase #3 $61.79   7.309%   $66.3062   $66.31   $66.30   $66.30  
  Purchase #4 $53.66   6.257%   $57.0175   $57.02   $57.00   $57.00  
  Purchase #5 $81.93   6.148%   $86.9671   $86.97   $86.95   $87.00  
  Purchase #6 $78.94   4.359%   $82.381   $82.38   $82.40   $82.40  
  Purchase #7 $13.98   10.184%   $15.4037   $15.40   $15.40   $15.40  
  7 purchase totals = $672.84       $726.7510   $726.75   $726.70   $726.80