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 $222.97   4.319%   $232.6001   $232.60   $232.60   $232.60  
  Purchase #2 $18.43   10.413%   $20.3491   $20.35   $20.35   $20.30  
  Purchase #3 $146.89   3.675%   $152.2882   $152.29   $152.30   $152.30  
  Purchase #4 $156.57   13.244%   $177.3061   $177.31   $177.30   $177.30  
  Purchase #5 $55.75   7.564%   $59.9669   $59.97   $59.95   $60.00  
  Purchase #6 $23.50   6.129%   $24.9403   $24.94   $24.95   $24.90  
  Purchase #7 $77.26   9.785%   $84.8199   $84.82   $84.80   $84.80  
  7 purchase totals = $701.37       $752.2706   $752.28   $752.25   $752.20