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 $230.31   13.652%   $261.7519   $261.75   $261.75   $261.80  
  Purchase #2 $228.57   3.168%   $235.8111   $235.81   $235.80   $235.80  
  Purchase #3 $100.63   5.741%   $106.4072   $106.41   $106.40   $106.40  
  Purchase #4 $59.57   11.363%   $66.3389   $66.34   $66.35   $66.30  
  Purchase #5 $229.28   11.872%   $256.5001   $256.50   $256.50   $256.50  
  Purchase #6 $25.93   10.834%   $28.7393   $28.74   $28.75   $28.70  
  Purchase #7 $81.41   5.604%   $85.9722   $85.97   $85.95   $86.00  
  7 purchase totals = $955.70       $1,041.5207   $1,041.52   $1,041.50   $1,041.50