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 $65.36   9.683%   $71.6888   $71.69   $71.70   $71.70  
  Purchase #2 $175.83   5.578%   $185.6378   $185.64   $185.65   $185.60  
  Purchase #3 $113.68   3.503%   $117.6622   $117.66   $117.65   $117.70  
  Purchase #4 $35.91   3.586%   $37.1977   $37.20   $37.20   $37.20  
  Purchase #5 $246.42   8.412%   $267.1489   $267.15   $267.15   $267.10  
  Purchase #6 $195.33   4.548%   $204.2136   $204.21   $204.20   $204.20  
  Purchase #7 $152.31   10.399%   $168.1487   $168.15   $168.15   $168.10  
  7 purchase totals = $984.84       $1,051.6977   $1,051.70   $1,051.70   $1,051.60