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 $42.69   10.466%   $47.1579   $47.16   $47.15   $47.20  
  Purchase #2 $116.68   6.401%   $124.1487   $124.15   $124.15   $124.10  
  Purchase #3 $132.25   3.566%   $136.966   $136.97   $136.95   $137.00  
  Purchase #4 $236.92   9.235%   $258.7996   $258.80   $258.80   $258.80  
  Purchase #5 $98.34   11.868%   $110.011   $110.01   $110.00   $110.00  
  Purchase #6 $176.84   8.567%   $191.9899   $191.99   $192.00   $192.00  
  Purchase #7 $15.50   3.208%   $15.9972   $16.00   $16.00   $16.00  
  7 purchase totals = $819.22       $885.0703   $885.08   $885.05   $885.10