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 $228.44   7.802%   $246.2629   $246.26   $246.25   $246.30  
  Purchase #2 $127.42   5.350%   $134.237   $134.24   $134.25   $134.20  
  Purchase #3 $45.42   3.730%   $47.1142   $47.11   $47.10   $47.10  
  Purchase #4 $177.99   7.380%   $191.1257   $191.13   $191.15   $191.10  
  Purchase #5 $89.36   9.265%   $97.6392   $97.64   $97.65   $97.60  
  Purchase #6 $58.34   9.736%   $64.02   $64.02   $64.00   $64.00  
  Purchase #7 $116.40   6.246%   $123.6703   $123.67   $123.65   $123.70  
  7 purchase totals = $843.37       $904.0693   $904.07   $904.05   $904.00