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 $46.82   9.647%   $51.3367   $51.34   $51.35   $51.30  
  Purchase #2 $101.57   13.430%   $115.2109   $115.21   $115.20   $115.20  
  Purchase #3 $204.98   3.709%   $212.5827   $212.58   $212.60   $212.60  
  Purchase #4 $132.34   11.748%   $147.8873   $147.89   $147.90   $147.90  
  Purchase #5 $96.40   6.778%   $102.934   $102.93   $102.95   $102.90  
  Purchase #6 $132.66   7.320%   $142.3707   $142.37   $142.35   $142.40  
  Purchase #7 $161.83   13.139%   $183.0928   $183.09   $183.10   $183.10  
  7 purchase totals = $876.60       $955.4151   $955.41   $955.45   $955.40