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 $248.91   10.718%   $275.5882   $275.59   $275.60   $275.60  
  Purchase #2 $89.72   5.709%   $94.8421   $94.84   $94.85   $94.80  
  Purchase #3 $37.57   11.280%   $41.8079   $41.81   $41.80   $41.80  
  Purchase #4 $5.27   13.583%   $5.9858   $5.99   $6.00   $6.00  
  Purchase #5 $80.63   4.370%   $84.1535   $84.15   $84.15   $84.20  
  Purchase #6 $176.42   13.798%   $200.7624   $200.76   $200.75   $200.80  
  Purchase #7 $110.49   12.661%   $124.4791   $124.48   $124.50   $124.50  
  7 purchase totals = $749.01       $827.6190   $827.62   $827.65   $827.70