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 $166.81   5.862%   $176.5884   $176.59   $176.60   $176.60  
  Purchase #2 $89.48   6.698%   $95.4734   $95.47   $95.45   $95.50  
  Purchase #3 $81.88   7.638%   $88.134   $88.13   $88.15   $88.10  
  Purchase #4 $84.74   9.684%   $92.9462   $92.95   $92.95   $92.90  
  Purchase #5 $181.70   8.643%   $197.4043   $197.40   $197.40   $197.40  
  Purchase #6 $86.72   3.391%   $89.6607   $89.66   $89.65   $89.70  
  Purchase #7 $155.71   13.384%   $176.5502   $176.55   $176.55   $176.60  
  7 purchase totals = $847.04       $916.7572   $916.75   $916.75   $916.80