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 $248.27   7.282%   $266.349   $266.35   $266.35   $266.30  
  Purchase #2 $25.53   9.426%   $27.9365   $27.94   $27.95   $27.90  
  Purchase #3 $13.79   6.624%   $14.7034   $14.70   $14.70   $14.70  
  Purchase #4 $98.92   4.832%   $103.6998   $103.70   $103.70   $103.70  
  Purchase #5 $130.30   8.304%   $141.1201   $141.12   $141.10   $141.10  
  Purchase #6 $81.97   9.257%   $89.558   $89.56   $89.55   $89.60  
  Purchase #7 $176.93   5.149%   $186.0401   $186.04   $186.05   $186.00  
  7 purchase totals = $775.71       $829.4069   $829.41   $829.40   $829.30