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 $67.46   3.410%   $69.7604   $69.76   $69.75   $69.80  
  Purchase #2 $77.76   11.729%   $86.8805   $86.88   $86.90   $86.90  
  Purchase #3 $15.43   5.658%   $16.303   $16.30   $16.30   $16.30  
  Purchase #4 $225.37   5.146%   $236.9675   $236.97   $236.95   $237.00  
  Purchase #5 $237.56   6.486%   $252.9681   $252.97   $252.95   $253.00  
  Purchase #6 $172.73   4.871%   $181.1437   $181.14   $181.15   $181.10  
  Purchase #7 $86.30   6.486%   $91.8974   $91.90   $91.90   $91.90  
  7 purchase totals = $882.61       $935.9206   $935.92   $935.90   $936.00