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 $60.36   11.470%   $67.2833   $67.28   $67.30   $67.30  
  Purchase #2 $54.99   13.275%   $62.2899   $62.29   $62.30   $62.30  
  Purchase #3 $194.62   7.324%   $208.874   $208.87   $208.85   $208.90  
  Purchase #4 $237.79   12.367%   $267.1975   $267.20   $267.20   $267.20  
  Purchase #5 $19.47   6.650%   $20.7648   $20.76   $20.75   $20.80  
  Purchase #6 $216.99   9.419%   $237.4283   $237.43   $237.45   $237.40  
  Purchase #7 $178.43   4.172%   $185.8741   $185.87   $185.85   $185.90  
  7 purchase totals = $962.65       $1,049.7119   $1,049.70   $1,049.70   $1,049.80