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 $206.86   13.413%   $234.6061   $234.61   $234.60   $234.60  
  Purchase #2 $43.73   3.660%   $45.3305   $45.33   $45.35   $45.30  
  Purchase #3 $118.39   12.443%   $133.1213   $133.12   $133.10   $133.10  
  Purchase #4 $245.89   3.289%   $253.9773   $253.98   $254.00   $254.00  
  Purchase #5 $41.69   10.609%   $46.1129   $46.11   $46.10   $46.10  
  Purchase #6 $195.45   5.524%   $206.2467   $206.25   $206.25   $206.20  
  Purchase #7 $68.45   6.364%   $72.8062   $72.81   $72.80   $72.80  
  7 purchase totals = $920.46       $992.2010   $992.21   $992.20   $992.10