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 $64.46   7.271%   $69.1469   $69.15   $69.15   $69.10  
  Purchase #2 $135.28   13.319%   $153.2979   $153.30   $153.30   $153.30  
  Purchase #3 $48.77   10.454%   $53.8684   $53.87   $53.85   $53.90  
  Purchase #4 $57.80   3.870%   $60.0369   $60.04   $60.05   $60.00  
  Purchase #5 $85.44   10.727%   $94.6051   $94.61   $94.60   $94.60  
  Purchase #6 $236.97   9.306%   $259.0224   $259.02   $259.00   $259.00  
  Purchase #7 $206.51   4.658%   $216.1292   $216.13   $216.15   $216.10  
  7 purchase totals = $835.23       $906.1068   $906.12   $906.10   $906.00