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 $235.95   10.596%   $260.9513   $260.95   $260.95   $261.00  
  Purchase #2 $17.71   12.638%   $19.9482   $19.95   $19.95   $19.90  
  Purchase #3 $166.27   10.566%   $183.8381   $183.84   $183.85   $183.80  
  Purchase #4 $94.79   6.834%   $101.2679   $101.27   $101.25   $101.30  
  Purchase #5 $54.73   11.260%   $60.8926   $60.89   $60.90   $60.90  
  Purchase #6 $173.47   11.433%   $193.3028   $193.30   $193.30   $193.30  
  Purchase #7 $23.89   6.152%   $25.3597   $25.36   $25.35   $25.40  
  7 purchase totals = $766.81       $845.5606   $845.56   $845.55   $845.60