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 $98.55   12.476%   $110.8451   $110.85   $110.85   $110.80  
  Purchase #2 $211.67   9.693%   $232.1872   $232.19   $232.20   $232.20  
  Purchase #3 $122.30   8.464%   $132.6515   $132.65   $132.65   $132.70  
  Purchase #4 $169.95   12.354%   $190.9456   $190.95   $190.95   $190.90  
  Purchase #5 $232.71   12.624%   $262.0873   $262.09   $262.10   $262.10  
  Purchase #6 $224.79   9.410%   $245.9427   $245.94   $245.95   $245.90  
  Purchase #7 $42.88   12.583%   $48.2756   $48.28   $48.30   $48.30  
  7 purchase totals = $1,102.85       $1,222.9350   $1,222.95   $1,223.00   $1,222.90