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 $239.28   11.407%   $266.5747   $266.57   $266.55   $266.60  
  Purchase #2 $208.26   8.374%   $225.6997   $225.70   $225.70   $225.70  
  Purchase #3 $248.65   5.487%   $262.2934   $262.29   $262.30   $262.30  
  Purchase #4 $183.36   3.692%   $190.1297   $190.13   $190.15   $190.10  
  Purchase #5 $170.80   7.228%   $183.1454   $183.15   $183.15   $183.10  
  Purchase #6 $110.45   10.619%   $122.1787   $122.18   $122.20   $122.20  
  Purchase #7 $161.42   12.424%   $181.4748   $181.47   $181.45   $181.50  
  7 purchase totals = $1,322.22       $1,431.4964   $1,431.49   $1,431.50   $1,431.50