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 $81.60   6.409%   $86.8297   $86.83   $86.85   $86.80  
  Purchase #2 $184.41   5.503%   $194.5581   $194.56   $194.55   $194.60  
  Purchase #3 $91.48   3.700%   $94.8648   $94.86   $94.85   $94.90  
  Purchase #4 $207.45   10.502%   $229.2364   $229.24   $229.25   $229.20  
  Purchase #5 $183.33   5.495%   $193.404   $193.40   $193.40   $193.40  
  Purchase #6 $84.51   12.186%   $94.8084   $94.81   $94.80   $94.80  
  Purchase #7 $135.38   3.141%   $139.6323   $139.63   $139.65   $139.60  
  7 purchase totals = $968.16       $1,033.3337   $1,033.33   $1,033.35   $1,033.30