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 $83.88   10.826%   $92.9608   $92.96   $92.95   $93.00  
  Purchase #2 $160.37   13.489%   $182.0023   $182.00   $182.00   $182.00  
  Purchase #3 $130.30   8.165%   $140.939   $140.94   $140.95   $140.90  
  Purchase #4 $91.94   6.574%   $97.9841   $97.98   $98.00   $98.00  
  Purchase #5 $222.91   7.854%   $240.4174   $240.42   $240.40   $240.40  
  Purchase #6 $70.31   5.124%   $73.9127   $73.91   $73.90   $73.90  
  Purchase #7 $28.42   5.375%   $29.9476   $29.95   $29.95   $29.90  
  7 purchase totals = $788.13       $858.1639   $858.16   $858.15   $858.10