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 $249.58   12.823%   $281.5836   $281.58   $281.60   $281.60  
  Purchase #2 $192.73   6.574%   $205.4001   $205.40   $205.40   $205.40  
  Purchase #3 $53.84   13.622%   $61.1741   $61.17   $61.15   $61.20  
  Purchase #4 $226.90   6.322%   $241.2446   $241.24   $241.25   $241.20  
  Purchase #5 $240.66   9.732%   $264.081   $264.08   $264.10   $264.10  
  Purchase #6 $202.30   4.509%   $211.4217   $211.42   $211.40   $211.40  
  Purchase #7 $172.38   6.750%   $184.0157   $184.02   $184.00   $184.00  
  7 purchase totals = $1,338.39       $1,448.9208   $1,448.91   $1,448.90   $1,448.90