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 $75.96   11.110%   $84.3992   $84.40   $84.40   $84.40  
  Purchase #2 $209.64   12.232%   $235.2832   $235.28   $235.30   $235.30  
  Purchase #3 $246.43   5.139%   $259.094   $259.09   $259.10   $259.10  
  Purchase #4 $92.78   5.759%   $98.1232   $98.12   $98.10   $98.10  
  Purchase #5 $153.67   12.606%   $173.0416   $173.04   $173.05   $173.00  
  Purchase #6 $236.56   7.293%   $253.8123   $253.81   $253.80   $253.80  
  Purchase #7 $240.87   5.384%   $253.8384   $253.84   $253.85   $253.80  
  7 purchase totals = $1,255.91       $1,357.5919   $1,357.58   $1,357.60   $1,357.50