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 $96.81   4.520%   $101.1858   $101.19   $101.20   $101.20  
  Purchase #2 $104.95   9.867%   $115.3054   $115.31   $115.30   $115.30  
  Purchase #3 $121.43   11.168%   $134.9913   $134.99   $135.00   $135.00  
  Purchase #4 $165.51   4.716%   $173.3155   $173.32   $173.30   $173.30  
  Purchase #5 $51.28   8.612%   $55.6962   $55.70   $55.70   $55.70  
  Purchase #6 $43.90   5.147%   $46.1595   $46.16   $46.15   $46.20  
  Purchase #7 $214.95   3.253%   $221.9423   $221.94   $221.95   $221.90  
  7 purchase totals = $798.83       $848.5960   $848.61   $848.60   $848.60