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 $185.71   4.846%   $194.7095   $194.71   $194.70   $194.70  
  Purchase #2 $57.92   8.783%   $63.0071   $63.01   $63.00   $63.00  
  Purchase #3 $140.71   10.440%   $155.4001   $155.40   $155.40   $155.40  
  Purchase #4 $207.63   6.276%   $220.6609   $220.66   $220.65   $220.70  
  Purchase #5 $78.63   4.147%   $81.8908   $81.89   $81.90   $81.90  
  Purchase #6 $183.57   10.116%   $202.1399   $202.14   $202.15   $202.10  
  Purchase #7 $167.62   4.797%   $175.6607   $175.66   $175.65   $175.70  
  7 purchase totals = $1,021.79       $1,093.4690   $1,093.47   $1,093.45   $1,093.50