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 $58.69   13.603%   $66.6736   $66.67   $66.65   $66.70  
  Purchase #2 $228.78   8.206%   $247.5537   $247.55   $247.55   $247.60  
  Purchase #3 $214.69   5.232%   $225.9226   $225.92   $225.90   $225.90  
  Purchase #4 $117.74   13.701%   $133.8716   $133.87   $133.85   $133.90  
  Purchase #5 $44.77   10.182%   $49.3285   $49.33   $49.35   $49.30  
  Purchase #6 $169.30   10.618%   $187.2763   $187.28   $187.30   $187.30  
  Purchase #7 $15.58   4.418%   $16.2683   $16.27   $16.25   $16.30  
  7 purchase totals = $849.55       $926.8946   $926.89   $926.85   $927.00