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 $182.95   12.422%   $205.676   $205.68   $205.70   $205.70  
  Purchase #2 $108.48   9.536%   $118.8247   $118.82   $118.80   $118.80  
  Purchase #3 $101.79   10.551%   $112.5299   $112.53   $112.55   $112.50  
  Purchase #4 $233.68   12.253%   $262.3128   $262.31   $262.30   $262.30  
  Purchase #5 $219.88   6.314%   $233.7632   $233.76   $233.75   $233.80  
  Purchase #6 $75.28   12.620%   $84.7803   $84.78   $84.80   $84.80  
  Purchase #7 $147.99   6.433%   $157.5102   $157.51   $157.50   $157.50  
  7 purchase totals = $1,070.05       $1,175.3971   $1,175.39   $1,175.40   $1,175.40