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 $58.91   10.606%   $65.158   $65.16   $65.15   $65.20  
  Purchase #2 $164.70   11.272%   $183.265   $183.27   $183.25   $183.30  
  Purchase #3 $68.69   9.242%   $75.0383   $75.04   $75.05   $75.00  
  Purchase #4 $204.80   8.344%   $221.8885   $221.89   $221.90   $221.90  
  Purchase #5 $211.46   4.825%   $221.6629   $221.66   $221.65   $221.70  
  Purchase #6 $160.71   8.472%   $174.3254   $174.33   $174.35   $174.30  
  Purchase #7 $104.49   10.173%   $115.1198   $115.12   $115.10   $115.10  
  7 purchase totals = $973.76       $1,056.4579   $1,056.47   $1,056.45   $1,056.50