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 $212.74   9.618%   $233.2013   $233.20   $233.20   $233.20  
  Purchase #2 $230.52   7.253%   $247.2396   $247.24   $247.25   $247.20  
  Purchase #3 $135.56   9.792%   $148.834   $148.83   $148.85   $148.80  
  Purchase #4 $161.55   13.732%   $183.734   $183.73   $183.75   $183.70  
  Purchase #5 $158.84   9.514%   $173.952   $173.95   $173.95   $174.00  
  Purchase #6 $247.63   12.680%   $279.0295   $279.03   $279.05   $279.00  
  Purchase #7 $123.27   3.611%   $127.7213   $127.72   $127.70   $127.70  
  7 purchase totals = $1,270.11       $1,393.7117   $1,393.70   $1,393.75   $1,393.60