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 $249.45   6.772%   $266.3428   $266.34   $266.35   $266.30  
  Purchase #2 $225.45   12.769%   $254.2377   $254.24   $254.25   $254.20  
  Purchase #3 $44.47   5.223%   $46.7927   $46.79   $46.80   $46.80  
  Purchase #4 $215.38   13.679%   $244.8418   $244.84   $244.85   $244.80  
  Purchase #5 $51.56   6.210%   $54.7619   $54.76   $54.75   $54.80  
  Purchase #6 $109.91   7.668%   $118.3379   $118.34   $118.35   $118.30  
  Purchase #7 $200.93   3.606%   $208.1755   $208.18   $208.20   $208.20  
  7 purchase totals = $1,097.15       $1,193.4903   $1,193.49   $1,193.55   $1,193.40