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 $221.74   10.172%   $244.2954   $244.30   $244.30   $244.30  
  Purchase #2 $146.95   7.268%   $157.6303   $157.63   $157.65   $157.60  
  Purchase #3 $219.94   7.695%   $236.8644   $236.86   $236.85   $236.90  
  Purchase #4 $235.26   13.582%   $267.213   $267.21   $267.20   $267.20  
  Purchase #5 $173.82   13.602%   $197.463   $197.46   $197.45   $197.50  
  Purchase #6 $21.78   9.625%   $23.8763   $23.88   $23.90   $23.90  
  Purchase #7 $212.41   11.702%   $237.2662   $237.27   $237.25   $237.30  
  7 purchase totals = $1,231.90       $1,364.6086   $1,364.61   $1,364.60   $1,364.70