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 $197.45   12.209%   $221.5567   $221.56   $221.55   $221.60  
  Purchase #2 $92.95   11.246%   $103.4032   $103.40   $103.40   $103.40  
  Purchase #3 $174.26   5.166%   $183.2623   $183.26   $183.25   $183.30  
  Purchase #4 $79.52   10.727%   $88.0501   $88.05   $88.05   $88.10  
  Purchase #5 $148.53   12.555%   $167.1779   $167.18   $167.20   $167.20  
  Purchase #6 $13.84   9.389%   $15.1394   $15.14   $15.15   $15.10  
  Purchase #7 $100.30   4.663%   $104.977   $104.98   $105.00   $105.00  
  7 purchase totals = $806.85       $883.5666   $883.57   $883.60   $883.70