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 $131.27   12.166%   $147.2403   $147.24   $147.25   $147.20  
  Purchase #2 $159.81   9.307%   $174.6835   $174.68   $174.70   $174.70  
  Purchase #3 $66.51   10.115%   $73.2375   $73.24   $73.25   $73.20  
  Purchase #4 $118.99   4.425%   $124.2553   $124.26   $124.25   $124.30  
  Purchase #5 $179.68   4.482%   $187.7333   $187.73   $187.75   $187.70  
  Purchase #6 $161.50   13.375%   $183.1006   $183.10   $183.10   $183.10  
  Purchase #7 $189.59   3.271%   $195.7915   $195.79   $195.80   $195.80  
  7 purchase totals = $1,007.35       $1,086.0420   $1,086.04   $1,086.10   $1,086.00