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 $71.76   10.156%   $79.0479   $79.05   $79.05   $79.00  
  Purchase #2 $195.46   7.258%   $209.6465   $209.65   $209.65   $209.60  
  Purchase #3 $116.90   7.545%   $125.7201   $125.72   $125.70   $125.70  
  Purchase #4 $86.29   12.609%   $97.1703   $97.17   $97.15   $97.20  
  Purchase #5 $237.59   11.610%   $265.1742   $265.17   $265.15   $265.20  
  Purchase #6 $133.78   13.294%   $151.5647   $151.56   $151.55   $151.60  
  Purchase #7 $160.84   4.163%   $167.5358   $167.54   $167.55   $167.50  
  7 purchase totals = $1,002.62       $1,095.8595   $1,095.86   $1,095.80   $1,095.80