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 $56.62   5.220%   $59.5756   $59.58   $59.60   $59.60  
  Purchase #2 $77.44   4.762%   $81.1277   $81.13   $81.15   $81.10  
  Purchase #3 $130.85   11.761%   $146.2393   $146.24   $146.25   $146.20  
  Purchase #4 $165.78   10.691%   $183.5035   $183.50   $183.50   $183.50  
  Purchase #5 $213.34   9.571%   $233.7588   $233.76   $233.75   $233.80  
  Purchase #6 $178.41   3.491%   $184.6383   $184.64   $184.65   $184.60  
  Purchase #7 $139.35   5.713%   $147.3111   $147.31   $147.30   $147.30  
  7 purchase totals = $961.79       $1,036.1543   $1,036.16   $1,036.20   $1,036.10