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 $44.97   3.138%   $46.3812   $46.38   $46.40   $46.40  
  Purchase #2 $24.90   10.847%   $27.6009   $27.60   $27.60   $27.60  
  Purchase #3 $207.36   12.772%   $233.844   $233.84   $233.85   $233.80  
  Purchase #4 $86.82   11.617%   $96.9059   $96.91   $96.90   $96.90  
  Purchase #5 $41.47   12.274%   $46.56   $46.56   $46.55   $46.60  
  Purchase #6 $126.84   7.560%   $136.4291   $136.43   $136.45   $136.40  
  Purchase #7 $61.59   5.237%   $64.8155   $64.82   $64.80   $64.80  
  7 purchase totals = $593.95       $652.5366   $652.54   $652.55   $652.50