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 $204.81   8.292%   $221.7928   $221.79   $221.80   $221.80  
  Purchase #2 $93.51   5.114%   $98.2921   $98.29   $98.30   $98.30  
  Purchase #3 $97.90   4.833%   $102.6315   $102.63   $102.65   $102.60  
  Purchase #4 $237.43   8.195%   $256.8874   $256.89   $256.90   $256.90  
  Purchase #5 $82.42   5.398%   $86.869   $86.87   $86.85   $86.90  
  Purchase #6 $220.73   8.810%   $240.1763   $240.18   $240.20   $240.20  
  Purchase #7 $214.73   6.358%   $228.3825   $228.38   $228.40   $228.40  
  7 purchase totals = $1,151.53       $1,235.0316   $1,235.03   $1,235.10   $1,235.10