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 $81.71   13.573%   $92.8005   $92.80   $92.80   $92.80  
  Purchase #2 $12.28   3.771%   $12.7431   $12.74   $12.75   $12.70  
  Purchase #3 $72.45   12.662%   $81.6236   $81.62   $81.60   $81.60  
  Purchase #4 $50.99   6.426%   $54.2666   $54.27   $54.25   $54.30  
  Purchase #5 $216.44   4.226%   $225.5868   $225.59   $225.60   $225.60  
  Purchase #6 $31.87   13.175%   $36.0689   $36.07   $36.05   $36.10  
  Purchase #7 $207.69   6.820%   $221.8545   $221.85   $221.85   $221.90  
  7 purchase totals = $673.43       $724.9440   $724.94   $724.90   $725.00