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 $104.61   10.133%   $115.2101   $115.21   $115.20   $115.20  
  Purchase #2 $110.83   12.456%   $124.635   $124.64   $124.65   $124.60  
  Purchase #3 $64.32   4.122%   $66.9713   $66.97   $66.95   $67.00  
  Purchase #4 $228.76   11.685%   $255.4906   $255.49   $255.50   $255.50  
  Purchase #5 $65.84   13.477%   $74.7133   $74.71   $74.70   $74.70  
  Purchase #6 $70.54   13.169%   $79.8294   $79.83   $79.85   $79.80  
  Purchase #7 $204.62   7.266%   $219.4877   $219.49   $219.50   $219.50  
  7 purchase totals = $849.52       $936.3374   $936.34   $936.35   $936.30