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 $212.34   6.699%   $226.5647   $226.56   $226.55   $226.60  
  Purchase #2 $40.41   13.725%   $45.9563   $45.96   $45.95   $46.00  
  Purchase #3 $96.67   11.386%   $107.6768   $107.68   $107.70   $107.70  
  Purchase #4 $206.63   9.153%   $225.5428   $225.54   $225.55   $225.50  
  Purchase #5 $245.98   3.184%   $253.812   $253.81   $253.80   $253.80  
  Purchase #6 $247.43   13.348%   $280.457   $280.46   $280.45   $280.50  
  Purchase #7 $247.47   6.672%   $263.9812   $263.98   $264.00   $264.00  
  7 purchase totals = $1,296.93       $1,403.9908   $1,403.99   $1,404.00   $1,404.10