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 $52.43   5.800%   $55.4709   $55.47   $55.45   $55.50  
  Purchase #2 $207.51   9.621%   $227.4745   $227.47   $227.45   $227.50  
  Purchase #3 $18.41   12.595%   $20.7287   $20.73   $20.75   $20.70  
  Purchase #4 $87.50   11.407%   $97.4811   $97.48   $97.50   $97.50  
  Purchase #5 $238.88   11.746%   $266.9388   $266.94   $266.95   $266.90  
  Purchase #6 $243.97   6.633%   $260.1525   $260.15   $260.15   $260.20  
  Purchase #7 $93.33   13.618%   $106.0397   $106.04   $106.05   $106.00  
  7 purchase totals = $942.03       $1,034.2862   $1,034.28   $1,034.30   $1,034.30