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 $240.63   11.707%   $268.8006   $268.80   $268.80   $268.80  
  Purchase #2 $94.67   11.308%   $105.3753   $105.38   $105.40   $105.40  
  Purchase #3 $174.48   10.663%   $193.0848   $193.08   $193.10   $193.10  
  Purchase #4 $216.62   4.424%   $226.2033   $226.20   $226.20   $226.20  
  Purchase #5 $47.81   11.271%   $53.1987   $53.20   $53.20   $53.20  
  Purchase #6 $39.42   11.722%   $44.0408   $44.04   $44.05   $44.00  
  Purchase #7 $136.56   12.246%   $153.2831   $153.28   $153.30   $153.30  
  7 purchase totals = $950.19       $1,043.9866   $1,043.98   $1,044.05   $1,044.00