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 $63.49   13.401%   $71.9983   $72.00   $72.00   $72.00  
  Purchase #2 $246.38   6.870%   $263.3063   $263.31   $263.30   $263.30  
  Purchase #3 $128.46   10.516%   $141.9689   $141.97   $141.95   $142.00  
  Purchase #4 $200.36   10.574%   $221.5461   $221.55   $221.55   $221.50  
  Purchase #5 $51.74   9.275%   $56.5389   $56.54   $56.55   $56.50  
  Purchase #6 $120.76   3.367%   $124.826   $124.83   $124.85   $124.80  
  Purchase #7 $60.32   5.269%   $63.4983   $63.50   $63.50   $63.50  
  7 purchase totals = $871.51       $943.6828   $943.70   $943.70   $943.60