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 $149.26   4.833%   $156.4737   $156.47   $156.45   $156.50  
  Purchase #2 $51.42   8.212%   $55.6426   $55.64   $55.65   $55.60  
  Purchase #3 $115.82   5.151%   $121.7859   $121.79   $121.80   $121.80  
  Purchase #4 $125.44   4.874%   $131.5539   $131.55   $131.55   $131.60  
  Purchase #5 $243.91   9.205%   $266.3619   $266.36   $266.35   $266.40  
  Purchase #6 $173.46   8.654%   $188.4712   $188.47   $188.45   $188.50  
  Purchase #7 $59.74   8.343%   $64.7241   $64.72   $64.70   $64.70  
  7 purchase totals = $919.05       $985.0133   $985.00   $984.95   $985.10