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 $65.84   11.242%   $73.2417   $73.24   $73.25   $73.20  
  Purchase #2 $207.36   6.275%   $220.3718   $220.37   $220.35   $220.40  
  Purchase #3 $201.26   11.334%   $224.0708   $224.07   $224.05   $224.10  
  Purchase #4 $57.41   7.515%   $61.7244   $61.72   $61.70   $61.70  
  Purchase #5 $243.58   9.591%   $266.9418   $266.94   $266.95   $266.90  
  Purchase #6 $13.79   13.251%   $15.6173   $15.62   $15.60   $15.60  
  Purchase #7 $8.47   4.232%   $8.8285   $8.83   $8.85   $8.80  
  7 purchase totals = $797.71       $870.7963   $870.79   $870.75   $870.70