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 $91.49   13.266%   $103.6271   $103.63   $103.65   $103.60  
  Purchase #2 $244.69   9.347%   $267.5612   $267.56   $267.55   $267.60  
  Purchase #3 $84.98   11.501%   $94.7535   $94.75   $94.75   $94.80  
  Purchase #4 $37.31   10.294%   $41.1507   $41.15   $41.15   $41.20  
  Purchase #5 $172.31   6.643%   $183.7566   $183.76   $183.75   $183.80  
  Purchase #6 $118.26   12.558%   $133.1111   $133.11   $133.10   $133.10  
  Purchase #7 $34.26   8.763%   $37.2622   $37.26   $37.25   $37.30  
  7 purchase totals = $783.30       $861.2224   $861.22   $861.20   $861.40