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 $248.65   8.306%   $269.3029   $269.30   $269.30   $269.30  
  Purchase #2 $200.56   6.503%   $213.6024   $213.60   $213.60   $213.60  
  Purchase #3 $160.70   6.509%   $171.16   $171.16   $171.15   $171.20  
  Purchase #4 $36.53   13.215%   $41.3574   $41.36   $41.35   $41.40  
  Purchase #5 $118.76   4.874%   $124.5484   $124.55   $124.55   $124.50  
  Purchase #6 $191.28   7.356%   $205.3506   $205.35   $205.35   $205.40  
  Purchase #7 $247.77   11.406%   $276.0306   $276.03   $276.05   $276.00  
  7 purchase totals = $1,204.25       $1,301.3523   $1,301.35   $1,301.35   $1,301.40