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 $246.42   3.857%   $255.9244   $255.92   $255.90   $255.90  
  Purchase #2 $135.53   9.863%   $148.8973   $148.90   $148.90   $148.90  
  Purchase #3 $31.37   3.552%   $32.4843   $32.48   $32.50   $32.50  
  Purchase #4 $210.65   11.249%   $234.346   $234.35   $234.35   $234.30  
  Purchase #5 $161.27   13.552%   $183.1253   $183.13   $183.15   $183.10  
  Purchase #6 $88.86   8.394%   $96.3189   $96.32   $96.30   $96.30  
  Purchase #7 $71.72   6.750%   $76.5611   $76.56   $76.55   $76.60  
  7 purchase totals = $945.82       $1,027.6573   $1,027.66   $1,027.65   $1,027.60