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 $58.29   13.692%   $66.2711   $66.27   $66.25   $66.30  
  Purchase #2 $221.29   9.700%   $242.7551   $242.76   $242.75   $242.80  
  Purchase #3 $199.45   5.874%   $211.1657   $211.17   $211.15   $211.20  
  Purchase #4 $120.49   12.650%   $135.732   $135.73   $135.75   $135.70  
  Purchase #5 $45.85   9.707%   $50.3007   $50.30   $50.30   $50.30  
  Purchase #6 $131.69   13.345%   $149.264   $149.26   $149.25   $149.30  
  Purchase #7 $111.68   13.707%   $126.988   $126.99   $127.00   $127.00  
  7 purchase totals = $888.74       $982.4766   $982.48   $982.45   $982.60