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 $239.94   13.627%   $272.6366   $272.64   $272.65   $272.60  
  Purchase #2 $43.75   9.375%   $47.8516   $47.85   $47.85   $47.90  
  Purchase #3 $177.26   10.326%   $195.5639   $195.56   $195.55   $195.60  
  Purchase #4 $219.89   3.347%   $227.2497   $227.25   $227.25   $227.20  
  Purchase #5 $177.85   13.217%   $201.3564   $201.36   $201.35   $201.40  
  Purchase #6 $118.69   5.226%   $124.8927   $124.89   $124.90   $124.90  
  Purchase #7 $63.64   4.801%   $66.6954   $66.70   $66.70   $66.70  
  7 purchase totals = $1,041.02       $1,136.2463   $1,136.25   $1,136.25   $1,136.30