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 $94.54   9.194%   $103.232   $103.23   $103.25   $103.20  
  Purchase #2 $226.33   11.561%   $252.496   $252.50   $252.50   $252.50  
  Purchase #3 $21.87   9.209%   $23.884   $23.88   $23.90   $23.90  
  Purchase #4 $95.88   10.581%   $106.0251   $106.03   $106.05   $106.00  
  Purchase #5 $17.92   5.192%   $18.8504   $18.85   $18.85   $18.90  
  Purchase #6 $58.48   6.579%   $62.3274   $62.33   $62.35   $62.30  
  Purchase #7 $151.75   10.379%   $167.5001   $167.50   $167.50   $167.50  
  7 purchase totals = $666.77       $734.3150   $734.32   $734.40   $734.30