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 $246.35   4.636%   $257.7708   $257.77   $257.75   $257.80  
  Purchase #2 $243.76   9.646%   $267.2731   $267.27   $267.25   $267.30  
  Purchase #3 $242.46   13.569%   $275.3594   $275.36   $275.35   $275.40  
  Purchase #4 $183.92   12.471%   $206.8567   $206.86   $206.85   $206.90  
  Purchase #5 $167.54   7.615%   $180.2982   $180.30   $180.30   $180.30  
  Purchase #6 $223.40   8.204%   $241.7277   $241.73   $241.75   $241.70  
  Purchase #7 $59.81   8.132%   $64.6737   $64.67   $64.65   $64.70  
  7 purchase totals = $1,367.24       $1,493.9596   $1,493.96   $1,493.90   $1,494.10