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 $237.99   11.594%   $265.5826   $265.58   $265.60   $265.60  
  Purchase #2 $85.73   12.379%   $96.3425   $96.34   $96.35   $96.30  
  Purchase #3 $195.96   4.583%   $204.9408   $204.94   $204.95   $204.90  
  Purchase #4 $247.63   12.521%   $278.6358   $278.64   $278.65   $278.60  
  Purchase #5 $162.49   10.528%   $179.5969   $179.60   $179.60   $179.60  
  Purchase #6 $85.91   11.384%   $95.69   $95.69   $95.70   $95.70  
  Purchase #7 $115.51   12.575%   $130.0354   $130.04   $130.05   $130.00  
  7 purchase totals = $1,131.22       $1,250.8240   $1,250.83   $1,250.90   $1,250.70