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 $61.30   11.471%   $68.3317   $68.33   $68.35   $68.30  
  Purchase #2 $144.43   4.470%   $150.886   $150.89   $150.90   $150.90  
  Purchase #3 $242.42   9.188%   $264.6935   $264.69   $264.70   $264.70  
  Purchase #4 $64.99   6.658%   $69.317   $69.32   $69.30   $69.30  
  Purchase #5 $18.61   11.672%   $20.7822   $20.78   $20.80   $20.80  
  Purchase #6 $159.33   11.226%   $177.2164   $177.22   $177.20   $177.20  
  Purchase #7 $94.65   11.741%   $105.7629   $105.76   $105.75   $105.80  
  7 purchase totals = $785.73       $856.9897   $856.99   $857.00   $857.00