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 $60.41   8.616%   $65.6149   $65.61   $65.60   $65.60  
  Purchase #2 $32.65   5.550%   $34.4621   $34.46   $34.45   $34.50  
  Purchase #3 $169.41   4.106%   $176.366   $176.37   $176.35   $176.40  
  Purchase #4 $199.55   10.563%   $220.6285   $220.63   $220.65   $220.60  
  Purchase #5 $247.65   11.345%   $275.7459   $275.75   $275.75   $275.70  
  Purchase #6 $229.80   10.249%   $253.3522   $253.35   $253.35   $253.40  
  Purchase #7 $240.29   3.814%   $249.4547   $249.45   $249.45   $249.50  
  7 purchase totals = $1,179.76       $1,275.6243   $1,275.62   $1,275.60   $1,275.70