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 $228.63   5.396%   $240.9669   $240.97   $240.95   $241.00  
  Purchase #2 $163.75   8.167%   $177.1235   $177.12   $177.10   $177.10  
  Purchase #3 $229.37   12.109%   $257.1444   $257.14   $257.15   $257.10  
  Purchase #4 $230.95   9.570%   $253.0519   $253.05   $253.05   $253.10  
  Purchase #5 $138.90   13.153%   $157.1695   $157.17   $157.15   $157.20  
  Purchase #6 $166.36   6.606%   $177.3497   $177.35   $177.35   $177.30  
  Purchase #7 $46.46   5.414%   $48.9753   $48.98   $49.00   $49.00  
  7 purchase totals = $1,204.42       $1,311.7812   $1,311.78   $1,311.75   $1,311.80