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 $190.86   8.728%   $207.5183   $207.52   $207.50   $207.50  
  Purchase #2 $198.37   11.788%   $221.7539   $221.75   $221.75   $221.80  
  Purchase #3 $23.68   12.853%   $26.7236   $26.72   $26.70   $26.70  
  Purchase #4 $104.66   13.327%   $118.608   $118.61   $118.60   $118.60  
  Purchase #5 $233.99   13.796%   $266.2713   $266.27   $266.25   $266.30  
  Purchase #6 $119.67   13.844%   $136.2371   $136.24   $136.25   $136.20  
  Purchase #7 $220.85   11.522%   $246.2963   $246.30   $246.30   $246.30  
  7 purchase totals = $1,092.08       $1,223.4085   $1,223.41   $1,223.35   $1,223.40