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 $56.49   8.534%   $61.3109   $61.31   $61.30   $61.30  
  Purchase #2 $24.32   6.596%   $25.9241   $25.92   $25.90   $25.90  
  Purchase #3 $58.30   8.144%   $63.048   $63.05   $63.05   $63.00  
  Purchase #4 $239.35   9.306%   $261.6239   $261.62   $261.60   $261.60  
  Purchase #5 $193.97   3.797%   $201.335   $201.34   $201.35   $201.30  
  Purchase #6 $187.49   5.326%   $197.4757   $197.48   $197.50   $197.50  
  Purchase #7 $58.70   7.584%   $63.1518   $63.15   $63.15   $63.20  
  7 purchase totals = $818.62       $873.8694   $873.87   $873.85   $873.80