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 $47.72   9.537%   $52.2711   $52.27   $52.25   $52.30  
  Purchase #2 $16.51   5.128%   $17.3566   $17.36   $17.35   $17.40  
  Purchase #3 $235.43   4.507%   $246.0408   $246.04   $246.05   $246.00  
  Purchase #4 $35.36   3.464%   $36.5849   $36.58   $36.60   $36.60  
  Purchase #5 $177.88   10.503%   $196.5627   $196.56   $196.55   $196.60  
  Purchase #6 $118.97   6.742%   $126.991   $126.99   $127.00   $127.00  
  Purchase #7 $32.44   8.338%   $35.1448   $35.14   $35.15   $35.10  
  7 purchase totals = $664.31       $710.9519   $710.94   $710.95   $711.00