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 $115.56   9.192%   $126.1823   $126.18   $126.20   $126.20  
  Purchase #2 $50.91   5.324%   $53.6204   $53.62   $53.60   $53.60  
  Purchase #3 $229.89   3.137%   $237.1016   $237.10   $237.10   $237.10  
  Purchase #4 $209.83   13.459%   $238.071   $238.07   $238.05   $238.10  
  Purchase #5 $89.89   9.248%   $98.203   $98.20   $98.20   $98.20  
  Purchase #6 $243.64   5.203%   $256.3166   $256.32   $256.30   $256.30  
  Purchase #7 $21.90   12.661%   $24.6728   $24.67   $24.65   $24.70  
  7 purchase totals = $961.62       $1,034.1677   $1,034.16   $1,034.10   $1,034.20