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 $115.94   9.312%   $126.7363   $126.74   $126.75   $126.70  
  Purchase #2 $74.85   13.251%   $84.7684   $84.77   $84.75   $84.80  
  Purchase #3 $97.76   8.199%   $105.7753   $105.78   $105.80   $105.80  
  Purchase #4 $245.67   6.665%   $262.0439   $262.04   $262.05   $262.00  
  Purchase #5 $178.60   9.173%   $194.983   $194.98   $195.00   $195.00  
  Purchase #6 $175.99   8.248%   $190.5057   $190.51   $190.50   $190.50  
  Purchase #7 $20.26   12.535%   $22.7996   $22.80   $22.80   $22.80  
  7 purchase totals = $909.07       $987.6122   $987.62   $987.65   $987.60