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 $64.87   4.227%   $67.6121   $67.61   $67.60   $67.60  
  Purchase #2 $93.33   5.706%   $98.6554   $98.66   $98.65   $98.70  
  Purchase #3 $156.85   4.258%   $163.5287   $163.53   $163.55   $163.50  
  Purchase #4 $87.98   4.855%   $92.2514   $92.25   $92.25   $92.30  
  Purchase #5 $205.70   3.513%   $212.9262   $212.93   $212.95   $212.90  
  Purchase #6 $213.37   7.503%   $229.3792   $229.38   $229.40   $229.40  
  Purchase #7 $203.53   6.689%   $217.1441   $217.14   $217.15   $217.10  
  7 purchase totals = $1,025.63       $1,081.4971   $1,081.50   $1,081.55   $1,081.50