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 $63.87   5.119%   $67.1395   $67.14   $67.15   $67.10  
  Purchase #2 $220.67   7.539%   $237.3063   $237.31   $237.30   $237.30  
  Purchase #3 $228.54   12.754%   $257.688   $257.69   $257.70   $257.70  
  Purchase #4 $217.63   5.804%   $230.2612   $230.26   $230.25   $230.30  
  Purchase #5 $25.56   4.752%   $26.7746   $26.77   $26.75   $26.80  
  Purchase #6 $195.73   10.837%   $216.9413   $216.94   $216.95   $216.90  
  Purchase #7 $13.48   5.856%   $14.2694   $14.27   $14.25   $14.30  
  7 purchase totals = $965.48       $1,050.3803   $1,050.38   $1,050.35   $1,050.40