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 $222.53   9.345%   $243.3254   $243.33   $243.35   $243.30  
  Purchase #2 $162.87   10.126%   $179.3622   $179.36   $179.35   $179.40  
  Purchase #3 $86.81   9.411%   $94.9797   $94.98   $95.00   $95.00  
  Purchase #4 $249.62   10.405%   $275.593   $275.59   $275.60   $275.60  
  Purchase #5 $138.75   9.222%   $151.5455   $151.55   $151.55   $151.50  
  Purchase #6 $189.53   11.659%   $211.6273   $211.63   $211.65   $211.60  
  Purchase #7 $239.78   13.475%   $272.0904   $272.09   $272.10   $272.10  
  7 purchase totals = $1,289.89       $1,428.5235   $1,428.53   $1,428.60   $1,428.50