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 $58.27   12.849%   $65.7571   $65.76   $65.75   $65.80  
  Purchase #2 $110.49   10.492%   $122.0826   $122.08   $122.10   $122.10  
  Purchase #3 $159.80   8.495%   $173.375   $173.38   $173.40   $173.40  
  Purchase #4 $175.54   11.254%   $195.2953   $195.30   $195.30   $195.30  
  Purchase #5 $239.39   12.263%   $268.7464   $268.75   $268.75   $268.70  
  Purchase #6 $85.87   9.752%   $94.244   $94.24   $94.25   $94.20  
  Purchase #7 $83.86   12.136%   $94.0372   $94.04   $94.05   $94.00  
  7 purchase totals = $913.22       $1,013.5376   $1,013.55   $1,013.60   $1,013.50