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 $244.72   11.811%   $273.6239   $273.62   $273.60   $273.60  
  Purchase #2 $242.80   8.163%   $262.6198   $262.62   $262.60   $262.60  
  Purchase #3 $121.91   3.701%   $126.4219   $126.42   $126.40   $126.40  
  Purchase #4 $201.54   9.518%   $220.7226   $220.72   $220.70   $220.70  
  Purchase #5 $187.64   10.130%   $206.6479   $206.65   $206.65   $206.60  
  Purchase #6 $109.38   10.407%   $120.7632   $120.76   $120.75   $120.80  
  Purchase #7 $155.70   7.286%   $167.0443   $167.04   $167.05   $167.00  
  7 purchase totals = $1,263.69       $1,377.8436   $1,377.83   $1,377.75   $1,377.70