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 $63.47   12.703%   $71.5326   $71.53   $71.55   $71.50  
  Purchase #2 $119.89   5.157%   $126.0727   $126.07   $126.05   $126.10  
  Purchase #3 $180.41   12.762%   $203.4339   $203.43   $203.45   $203.40  
  Purchase #4 $16.29   11.787%   $18.2101   $18.21   $18.20   $18.20  
  Purchase #5 $216.54   12.681%   $243.9994   $244.00   $244.00   $244.00  
  Purchase #6 $15.29   6.366%   $16.2634   $16.26   $16.25   $16.30  
  Purchase #7 $79.36   8.161%   $85.8366   $85.84   $85.85   $85.80  
  7 purchase totals = $691.25       $765.3487   $765.34   $765.35   $765.30