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 $237.48   10.589%   $262.6268   $262.63   $262.65   $262.60  
  Purchase #2 $192.48   8.497%   $208.835   $208.84   $208.85   $208.80  
  Purchase #3 $207.96   7.359%   $223.2638   $223.26   $223.25   $223.30  
  Purchase #4 $56.56   13.803%   $64.367   $64.37   $64.35   $64.40  
  Purchase #5 $179.53   11.335%   $199.8797   $199.88   $199.90   $199.90  
  Purchase #6 $13.36   10.114%   $14.7112   $14.71   $14.70   $14.70  
  Purchase #7 $80.58   11.210%   $89.613   $89.61   $89.60   $89.60  
  7 purchase totals = $967.95       $1,063.2965   $1,063.30   $1,063.30   $1,063.30