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 $13.27   8.443%   $14.3904   $14.39   $14.40   $14.40  
  Purchase #2 $193.41   3.145%   $199.4927   $199.49   $199.50   $199.50  
  Purchase #3 $117.50   12.359%   $132.0218   $132.02   $132.00   $132.00  
  Purchase #4 $7.30   10.408%   $8.0598   $8.06   $8.05   $8.10  
  Purchase #5 $17.95   3.456%   $18.5704   $18.57   $18.55   $18.60  
  Purchase #6 $169.46   10.824%   $187.8024   $187.80   $187.80   $187.80  
  Purchase #7 $114.83   7.439%   $123.3722   $123.37   $123.35   $123.40  
  7 purchase totals = $633.72       $683.7097   $683.70   $683.65   $683.80