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 $196.51   9.298%   $214.7815   $214.78   $214.80   $214.80  
  Purchase #2 $55.63   12.598%   $62.6383   $62.64   $62.65   $62.60  
  Purchase #3 $83.88   11.431%   $93.4683   $93.47   $93.45   $93.50  
  Purchase #4 $120.73   7.591%   $129.8946   $129.89   $129.90   $129.90  
  Purchase #5 $67.84   4.139%   $70.6479   $70.65   $70.65   $70.60  
  Purchase #6 $38.84   10.450%   $42.8988   $42.90   $42.90   $42.90  
  Purchase #7 $234.37   7.467%   $251.8704   $251.87   $251.85   $251.90  
  7 purchase totals = $797.80       $866.1998   $866.20   $866.20   $866.20