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 $195.30   8.245%   $211.4025   $211.40   $211.40   $211.40  
  Purchase #2 $62.79   10.722%   $69.5223   $69.52   $69.50   $69.50  
  Purchase #3 $250.99   4.822%   $263.0927   $263.09   $263.10   $263.10  
  Purchase #4 $93.97   8.302%   $101.7714   $101.77   $101.75   $101.80  
  Purchase #5 $71.40   7.328%   $76.6322   $76.63   $76.65   $76.60  
  Purchase #6 $11.83   3.284%   $12.2185   $12.22   $12.20   $12.20  
  Purchase #7 $180.73   6.855%   $193.119   $193.12   $193.10   $193.10  
  7 purchase totals = $867.01       $927.7586   $927.75   $927.70   $927.70