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 $8.60   13.236%   $9.7383   $9.74   $9.75   $9.70  
  Purchase #2 $85.81   10.713%   $95.0028   $95.00   $95.00   $95.00  
  Purchase #3 $104.33   6.602%   $111.2179   $111.22   $111.20   $111.20  
  Purchase #4 $183.27   12.488%   $206.1568   $206.16   $206.15   $206.20  
  Purchase #5 $169.92   12.361%   $190.9238   $190.92   $190.90   $190.90  
  Purchase #6 $126.29   12.757%   $142.4008   $142.40   $142.40   $142.40  
  Purchase #7 $150.97   11.267%   $167.9798   $167.98   $168.00   $168.00  
  7 purchase totals = $829.19       $923.4202   $923.42   $923.40   $923.40