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 $73.44   12.547%   $82.6545   $82.65   $82.65   $82.70  
  Purchase #2 $77.63   10.452%   $85.7439   $85.74   $85.75   $85.70  
  Purchase #3 $213.95   5.360%   $225.4177   $225.42   $225.40   $225.40  
  Purchase #4 $11.42   11.600%   $12.7447   $12.74   $12.75   $12.70  
  Purchase #5 $144.44   11.683%   $161.3149   $161.31   $161.30   $161.30  
  Purchase #6 $157.57   6.173%   $167.2968   $167.30   $167.30   $167.30  
  Purchase #7 $35.90   6.227%   $38.1355   $38.14   $38.15   $38.10  
  7 purchase totals = $714.35       $773.3080   $773.30   $773.30   $773.20