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 $182.43   5.701%   $192.8303   $192.83   $192.85   $192.80  
  Purchase #2 $237.82   8.351%   $257.6803   $257.68   $257.70   $257.70  
  Purchase #3 $86.88   8.404%   $94.1814   $94.18   $94.20   $94.20  
  Purchase #4 $90.94   7.783%   $98.0179   $98.02   $98.00   $98.00  
  Purchase #5 $50.28   13.399%   $57.017   $57.02   $57.00   $57.00  
  Purchase #6 $171.47   8.620%   $186.2507   $186.25   $186.25   $186.30  
  Purchase #7 $24.61   8.666%   $26.7427   $26.74   $26.75   $26.70  
  7 purchase totals = $844.43       $912.7203   $912.72   $912.75   $912.70