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 $60.38   13.302%   $68.4117   $68.41   $68.40   $68.40  
  Purchase #2 $175.81   8.559%   $190.8576   $190.86   $190.85   $190.90  
  Purchase #3 $149.65   9.711%   $164.1825   $164.18   $164.20   $164.20  
  Purchase #4 $159.94   5.298%   $168.4136   $168.41   $168.40   $168.40  
  Purchase #5 $182.88   12.404%   $205.5644   $205.56   $205.55   $205.60  
  Purchase #6 $73.44   8.782%   $79.8895   $79.89   $79.90   $79.90  
  Purchase #7 $140.98   9.279%   $154.0615   $154.06   $154.05   $154.10  
  7 purchase totals = $943.08       $1,031.3808   $1,031.37   $1,031.35   $1,031.50