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 $93.88   11.420%   $104.6011   $104.60   $104.60   $104.60  
  Purchase #2 $249.92   5.327%   $263.2332   $263.23   $263.25   $263.20  
  Purchase #3 $69.38   11.250%   $77.1853   $77.19   $77.20   $77.20  
  Purchase #4 $227.83   4.606%   $238.3238   $238.32   $238.30   $238.30  
  Purchase #5 $146.45   13.301%   $165.9293   $165.93   $165.95   $165.90  
  Purchase #6 $239.63   11.389%   $266.9215   $266.92   $266.90   $266.90  
  Purchase #7 $135.65   10.757%   $150.2419   $150.24   $150.25   $150.20  
  7 purchase totals = $1,162.74       $1,266.4361   $1,266.43   $1,266.45   $1,266.30