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 $84.28   13.623%   $95.7615   $95.76   $95.75   $95.80  
  Purchase #2 $93.66   10.773%   $103.75   $103.75   $103.75   $103.80  
  Purchase #3 $229.73   13.125%   $259.8821   $259.88   $259.90   $259.90  
  Purchase #4 $184.42   4.210%   $192.1841   $192.18   $192.20   $192.20  
  Purchase #5 $68.28   6.396%   $72.6472   $72.65   $72.65   $72.60  
  Purchase #6 $167.37   7.411%   $179.7738   $179.77   $179.75   $179.80  
  Purchase #7 $24.99   3.486%   $25.8612   $25.86   $25.85   $25.90  
  7 purchase totals = $852.73       $929.8599   $929.85   $929.85   $930.00