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 $227.52   11.291%   $253.2093   $253.21   $253.20   $253.20  
  Purchase #2 $90.35   3.588%   $93.5918   $93.59   $93.60   $93.60  
  Purchase #3 $88.68   10.518%   $98.0074   $98.01   $98.00   $98.00  
  Purchase #4 $28.33   8.107%   $30.6267   $30.63   $30.65   $30.60  
  Purchase #5 $237.30   8.423%   $257.2878   $257.29   $257.30   $257.30  
  Purchase #6 $19.49   5.625%   $20.5863   $20.59   $20.60   $20.60  
  Purchase #7 $39.39   6.642%   $42.0063   $42.01   $42.00   $42.00  
  7 purchase totals = $731.06       $795.3156   $795.33   $795.35   $795.30