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 $208.63   9.585%   $228.6272   $228.63   $228.65   $228.60  
  Purchase #2 $227.30   3.667%   $235.6351   $235.64   $235.65   $235.60  
  Purchase #3 $247.57   12.571%   $278.692   $278.69   $278.70   $278.70  
  Purchase #4 $18.90   3.565%   $19.5738   $19.57   $19.55   $19.60  
  Purchase #5 $179.36   8.673%   $194.9159   $194.92   $194.90   $194.90  
  Purchase #6 $13.29   11.582%   $14.8292   $14.83   $14.85   $14.80  
  Purchase #7 $249.63   11.206%   $277.6035   $277.60   $277.60   $277.60  
  7 purchase totals = $1,144.68       $1,249.8767   $1,249.88   $1,249.90   $1,249.80