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 $71.45   8.813%   $77.7469   $77.75   $77.75   $77.70  
  Purchase #2 $73.85   3.551%   $76.4724   $76.47   $76.45   $76.50  
  Purchase #3 $213.81   5.213%   $224.9559   $224.96   $224.95   $225.00  
  Purchase #4 $52.34   10.439%   $57.8038   $57.80   $57.80   $57.80  
  Purchase #5 $220.92   9.740%   $242.4376   $242.44   $242.45   $242.40  
  Purchase #6 $58.36   11.738%   $65.2103   $65.21   $65.20   $65.20  
  Purchase #7 $19.81   10.627%   $21.9152   $21.92   $21.90   $21.90  
  7 purchase totals = $710.54       $766.5421   $766.55   $766.50   $766.50