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 $55.97   11.335%   $62.3142   $62.31   $62.30   $62.30  
  Purchase #2 $165.54   5.328%   $174.36   $174.36   $174.35   $174.40  
  Purchase #3 $93.95   8.484%   $101.9207   $101.92   $101.90   $101.90  
  Purchase #4 $14.62   7.419%   $15.7047   $15.70   $15.70   $15.70  
  Purchase #5 $232.73   9.148%   $254.0201   $254.02   $254.00   $254.00  
  Purchase #6 $154.42   7.591%   $166.142   $166.14   $166.15   $166.10  
  Purchase #7 $42.85   7.837%   $46.2082   $46.21   $46.20   $46.20  
  7 purchase totals = $760.08       $820.6699   $820.66   $820.60   $820.60