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 $90.32   3.325%   $93.3231   $93.32   $93.30   $93.30  
  Purchase #2 $242.41   9.570%   $265.6086   $265.61   $265.60   $265.60  
  Purchase #3 $190.82   9.646%   $209.2265   $209.23   $209.25   $209.20  
  Purchase #4 $14.64   10.677%   $16.2031   $16.20   $16.20   $16.20  
  Purchase #5 $27.27   5.509%   $28.7723   $28.77   $28.75   $28.80  
  Purchase #6 $105.50   8.555%   $114.5255   $114.53   $114.55   $114.50  
  Purchase #7 $90.33   10.115%   $99.4669   $99.47   $99.45   $99.50  
  7 purchase totals = $761.29       $827.1260   $827.13   $827.10   $827.10