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 $194.45   5.781%   $205.6912   $205.69   $205.70   $205.70  
  Purchase #2 $37.87   11.117%   $42.08   $42.08   $42.10   $42.10  
  Purchase #3 $17.55   10.117%   $19.3255   $19.33   $19.35   $19.30  
  Purchase #4 $139.46   12.226%   $156.5104   $156.51   $156.50   $156.50  
  Purchase #5 $67.28   5.660%   $71.088   $71.09   $71.10   $71.10  
  Purchase #6 $185.53   11.115%   $206.1517   $206.15   $206.15   $206.20  
  Purchase #7 $179.44   10.261%   $197.8523   $197.85   $197.85   $197.90  
  7 purchase totals = $821.58       $898.6991   $898.70   $898.75   $898.80