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 $61.50   10.687%   $68.0725   $68.07   $68.05   $68.10  
  Purchase #2 $221.47   6.653%   $236.2044   $236.20   $236.20   $236.20  
  Purchase #3 $81.34   4.391%   $84.9116   $84.91   $84.90   $84.90  
  Purchase #4 $151.53   5.392%   $159.7005   $159.70   $159.70   $159.70  
  Purchase #5 $57.49   3.624%   $59.5734   $59.57   $59.55   $59.60  
  Purchase #6 $133.37   12.409%   $149.9199   $149.92   $149.90   $149.90  
  Purchase #7 $54.61   9.355%   $59.7188   $59.72   $59.70   $59.70  
  7 purchase totals = $761.31       $818.1011   $818.09   $818.00   $818.10