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 $65.54   12.218%   $73.5477   $73.55   $73.55   $73.50  
  Purchase #2 $164.46   8.356%   $178.2023   $178.20   $178.20   $178.20  
  Purchase #3 $8.74   13.856%   $9.951   $9.95   $9.95   $10.00  
  Purchase #4 $180.68   3.303%   $186.6479   $186.65   $186.65   $186.60  
  Purchase #5 $152.39   5.145%   $160.2305   $160.23   $160.25   $160.20  
  Purchase #6 $16.42   3.609%   $17.0126   $17.01   $17.00   $17.00  
  Purchase #7 $140.58   5.789%   $148.7182   $148.72   $148.70   $148.70  
  7 purchase totals = $728.81       $774.3102   $774.31   $774.30   $774.20