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 $62.44   4.854%   $65.4708   $65.47   $65.45   $65.50  
  Purchase #2 $51.62   4.612%   $54.0007   $54.00   $54.00   $54.00  
  Purchase #3 $148.95   8.702%   $161.9116   $161.91   $161.90   $161.90  
  Purchase #4 $244.76   5.162%   $257.3945   $257.39   $257.40   $257.40  
  Purchase #5 $246.53   11.452%   $274.7626   $274.76   $274.75   $274.80  
  Purchase #6 $68.43   6.494%   $72.8738   $72.87   $72.85   $72.90  
  Purchase #7 $135.40   4.346%   $141.2845   $141.28   $141.30   $141.30  
  7 purchase totals = $958.13       $1,027.6985   $1,027.68   $1,027.65   $1,027.80