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 $59.86   8.185%   $64.7595   $64.76   $64.75   $64.80  
  Purchase #2 $156.51   7.735%   $168.616   $168.62   $168.60   $168.60  
  Purchase #3 $211.80   8.567%   $229.9449   $229.94   $229.95   $229.90  
  Purchase #4 $19.94   13.669%   $22.6656   $22.67   $22.65   $22.70  
  Purchase #5 $204.56   8.453%   $221.8515   $221.85   $221.85   $221.90  
  Purchase #6 $103.87   10.803%   $115.0911   $115.09   $115.10   $115.10  
  Purchase #7 $29.51   5.390%   $31.1006   $31.10   $31.10   $31.10  
  7 purchase totals = $786.05       $854.0292   $854.03   $854.00   $854.10