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 $90.86   4.104%   $94.5889   $94.59   $94.60   $94.60  
  Purchase #2 $175.87   13.581%   $199.7549   $199.75   $199.75   $199.80  
  Purchase #3 $218.67   8.838%   $237.9961   $238.00   $238.00   $238.00  
  Purchase #4 $37.31   9.571%   $40.8809   $40.88   $40.90   $40.90  
  Purchase #5 $170.39   13.416%   $193.2495   $193.25   $193.25   $193.20  
  Purchase #6 $123.67   8.364%   $134.0138   $134.01   $134.00   $134.00  
  Purchase #7 $93.26   10.180%   $102.7539   $102.75   $102.75   $102.80  
  7 purchase totals = $910.03       $1,003.2380   $1,003.23   $1,003.25   $1,003.30