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 $85.98   8.424%   $93.223   $93.22   $93.20   $93.20  
  Purchase #2 $248.44   5.437%   $261.9477   $261.95   $261.95   $261.90  
  Purchase #3 $222.39   6.112%   $235.9825   $235.98   $236.00   $236.00  
  Purchase #4 $170.85   13.535%   $193.9745   $193.97   $193.95   $194.00  
  Purchase #5 $164.52   8.709%   $178.848   $178.85   $178.85   $178.80  
  Purchase #6 $46.47   6.287%   $49.3916   $49.39   $49.40   $49.40  
  Purchase #7 $65.46   13.450%   $74.2644   $74.26   $74.25   $74.30  
  7 purchase totals = $1,004.11       $1,087.6317   $1,087.62   $1,087.60   $1,087.60