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 $231.39   9.564%   $253.5201   $253.52   $253.50   $253.50  
  Purchase #2 $87.58   9.865%   $96.2198   $96.22   $96.20   $96.20  
  Purchase #3 $195.72   9.839%   $214.9769   $214.98   $215.00   $215.00  
  Purchase #4 $94.81   3.698%   $98.3161   $98.32   $98.30   $98.30  
  Purchase #5 $77.38   4.744%   $81.0509   $81.05   $81.05   $81.10  
  Purchase #6 $244.71   11.857%   $273.7253   $273.73   $273.75   $273.70  
  Purchase #7 $78.64   8.847%   $85.5973   $85.60   $85.60   $85.60  
  7 purchase totals = $1,010.23       $1,103.4064   $1,103.42   $1,103.40   $1,103.40