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 $60.82   13.687%   $69.1444   $69.14   $69.15   $69.10  
  Purchase #2 $221.96   5.687%   $234.5829   $234.58   $234.60   $234.60  
  Purchase #3 $209.29   7.128%   $224.2082   $224.21   $224.20   $224.20  
  Purchase #4 $175.61   4.345%   $183.2403   $183.24   $183.25   $183.20  
  Purchase #5 $130.39   12.211%   $146.3119   $146.31   $146.30   $146.30  
  Purchase #6 $34.88   11.144%   $38.767   $38.77   $38.75   $38.80  
  Purchase #7 $143.37   3.272%   $148.0611   $148.06   $148.05   $148.10  
  7 purchase totals = $976.32       $1,044.3158   $1,044.31   $1,044.30   $1,044.30