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 $207.66   6.509%   $221.1766   $221.18   $221.20   $221.20  
  Purchase #2 $61.50   11.147%   $68.3554   $68.36   $68.35   $68.40  
  Purchase #3 $184.46   13.644%   $209.6277   $209.63   $209.65   $209.60  
  Purchase #4 $132.68   9.773%   $145.6468   $145.65   $145.65   $145.60  
  Purchase #5 $202.80   10.338%   $223.7655   $223.77   $223.75   $223.80  
  Purchase #6 $108.69   8.127%   $117.5232   $117.52   $117.50   $117.50  
  Purchase #7 $188.73   3.162%   $194.6976   $194.70   $194.70   $194.70  
  7 purchase totals = $1,086.52       $1,180.7928   $1,180.81   $1,180.80   $1,180.80