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 $52.49   7.158%   $56.2472   $56.25   $56.25   $56.20  
  Purchase #2 $58.95   10.829%   $65.3337   $65.33   $65.35   $65.30  
  Purchase #3 $240.33   10.440%   $265.4205   $265.42   $265.40   $265.40  
  Purchase #4 $21.74   10.604%   $24.0453   $24.05   $24.05   $24.00  
  Purchase #5 $157.59   7.727%   $169.767   $169.77   $169.75   $169.80  
  Purchase #6 $197.60   8.619%   $214.6311   $214.63   $214.65   $214.60  
  Purchase #7 $11.40   4.515%   $11.9147   $11.91   $11.90   $11.90  
  7 purchase totals = $740.10       $807.3595   $807.36   $807.35   $807.20