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 $231.63   13.476%   $262.8445   $262.84   $262.85   $262.80  
  Purchase #2 $185.39   8.622%   $201.3743   $201.37   $201.35   $201.40  
  Purchase #3 $98.53   11.292%   $109.656   $109.66   $109.65   $109.70  
  Purchase #4 $23.32   4.422%   $24.3512   $24.35   $24.35   $24.40  
  Purchase #5 $244.51   7.678%   $263.2835   $263.28   $263.30   $263.30  
  Purchase #6 $23.42   3.767%   $24.3022   $24.30   $24.30   $24.30  
  Purchase #7 $178.62   11.483%   $199.1309   $199.13   $199.15   $199.10  
  7 purchase totals = $985.42       $1,084.9426   $1,084.93   $1,084.95   $1,085.00