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 $227.44   11.331%   $253.2112   $253.21   $253.20   $253.20  
  Purchase #2 $166.57   6.120%   $176.7641   $176.76   $176.75   $176.80  
  Purchase #3 $96.91   4.395%   $101.1692   $101.17   $101.15   $101.20  
  Purchase #4 $127.65   12.255%   $143.2935   $143.29   $143.30   $143.30  
  Purchase #5 $79.76   11.650%   $89.052   $89.05   $89.05   $89.10  
  Purchase #6 $197.25   11.803%   $220.5314   $220.53   $220.55   $220.50  
  Purchase #7 $86.37   6.161%   $91.6913   $91.69   $91.70   $91.70  
  7 purchase totals = $981.95       $1,075.7127   $1,075.70   $1,075.70   $1,075.80