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 $114.68   8.850%   $124.8292   $124.83   $124.85   $124.80  
  Purchase #2 $51.63   10.224%   $56.9087   $56.91   $56.90   $56.90  
  Purchase #3 $241.29   11.373%   $268.7319   $268.73   $268.75   $268.70  
  Purchase #4 $63.67   11.377%   $70.9137   $70.91   $70.90   $70.90  
  Purchase #5 $105.25   4.823%   $110.3262   $110.33   $110.35   $110.30  
  Purchase #6 $66.70   9.713%   $73.1786   $73.18   $73.20   $73.20  
  Purchase #7 $33.46   8.182%   $36.1977   $36.20   $36.20   $36.20  
  7 purchase totals = $676.68       $741.0860   $741.09   $741.15   $741.00