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 $151.76   6.674%   $161.8885   $161.89   $161.90   $161.90  
  Purchase #2 $235.63   13.518%   $267.4825   $267.48   $267.50   $267.50  
  Purchase #3 $75.62   5.319%   $79.6422   $79.64   $79.65   $79.60  
  Purchase #4 $207.41   3.575%   $214.8249   $214.82   $214.80   $214.80  
  Purchase #5 $131.64   10.591%   $145.582   $145.58   $145.60   $145.60  
  Purchase #6 $175.59   12.703%   $197.8952   $197.90   $197.90   $197.90  
  Purchase #7 $89.73   12.588%   $101.0252   $101.03   $101.05   $101.00  
  7 purchase totals = $1,067.38       $1,168.3405   $1,168.34   $1,168.40   $1,168.30