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 $241.56   11.577%   $269.5254   $269.53   $269.55   $269.50  
  Purchase #2 $167.41   3.493%   $173.2576   $173.26   $173.25   $173.30  
  Purchase #3 $146.44   7.467%   $157.3747   $157.37   $157.35   $157.40  
  Purchase #4 $250.76   11.328%   $279.1661   $279.17   $279.15   $279.20  
  Purchase #5 $51.53   8.368%   $55.842   $55.84   $55.85   $55.80  
  Purchase #6 $177.52   5.572%   $187.4114   $187.41   $187.40   $187.40  
  Purchase #7 $194.32   3.459%   $201.0415   $201.04   $201.05   $201.00  
  7 purchase totals = $1,229.54       $1,323.6187   $1,323.62   $1,323.60   $1,323.60