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 $83.74   12.631%   $94.3172   $94.32   $94.30   $94.30  
  Purchase #2 $54.51   7.696%   $58.7051   $58.71   $58.70   $58.70  
  Purchase #3 $119.77   10.707%   $132.5938   $132.59   $132.60   $132.60  
  Purchase #4 $195.66   7.302%   $209.9471   $209.95   $209.95   $209.90  
  Purchase #5 $16.81   11.830%   $18.7986   $18.80   $18.80   $18.80  
  Purchase #6 $53.62   3.210%   $55.3412   $55.34   $55.35   $55.30  
  Purchase #7 $248.62   7.587%   $267.4828   $267.48   $267.50   $267.50  
  7 purchase totals = $772.73       $837.1858   $837.19   $837.20   $837.10