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 $204.98   11.202%   $227.9419   $227.94   $227.95   $227.90  
  Purchase #2 $196.88   9.405%   $215.3966   $215.40   $215.40   $215.40  
  Purchase #3 $235.48   11.536%   $262.645   $262.65   $262.65   $262.60  
  Purchase #4 $88.84   5.554%   $93.7742   $93.77   $93.75   $93.80  
  Purchase #5 $126.69   8.139%   $137.0013   $137.00   $137.00   $137.00  
  Purchase #6 $60.88   5.270%   $64.0884   $64.09   $64.10   $64.10  
  Purchase #7 $42.47   9.192%   $46.3738   $46.37   $46.35   $46.40  
  7 purchase totals = $956.22       $1,047.2212   $1,047.22   $1,047.20   $1,047.20