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 $168.26   11.746%   $188.0238   $188.02   $188.00   $188.00  
  Purchase #2 $181.51   10.102%   $199.8461   $199.85   $199.85   $199.80  
  Purchase #3 $164.95   8.342%   $178.7101   $178.71   $178.70   $178.70  
  Purchase #4 $228.59   12.115%   $256.2837   $256.28   $256.30   $256.30  
  Purchase #5 $241.61   11.181%   $268.6244   $268.62   $268.60   $268.60  
  Purchase #6 $225.31   3.833%   $233.9461   $233.95   $233.95   $233.90  
  Purchase #7 $231.54   13.594%   $263.0155   $263.02   $263.00   $263.00  
  7 purchase totals = $1,441.77       $1,588.4497   $1,588.45   $1,588.40   $1,588.30