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 $197.58   12.121%   $221.5287   $221.53   $221.55   $221.50  
  Purchase #2 $161.61   4.766%   $169.3123   $169.31   $169.30   $169.30  
  Purchase #3 $200.77   5.186%   $211.1819   $211.18   $211.20   $211.20  
  Purchase #4 $71.58   6.558%   $76.2742   $76.27   $76.25   $76.30  
  Purchase #5 $105.64   6.389%   $112.3893   $112.39   $112.40   $112.40  
  Purchase #6 $178.69   4.348%   $186.4594   $186.46   $186.45   $186.50  
  Purchase #7 $15.31   6.147%   $16.2511   $16.25   $16.25   $16.30  
  7 purchase totals = $931.18       $993.3969   $993.39   $993.40   $993.50