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 $14.98   8.472%   $16.2491   $16.25   $16.25   $16.20  
  Purchase #2 $104.92   6.386%   $111.6202   $111.62   $111.60   $111.60  
  Purchase #3 $83.56   3.467%   $86.457   $86.46   $86.45   $86.50  
  Purchase #4 $42.65   7.290%   $45.7592   $45.76   $45.75   $45.80  
  Purchase #5 $79.64   7.441%   $85.566   $85.57   $85.55   $85.60  
  Purchase #6 $87.45   9.469%   $95.7306   $95.73   $95.75   $95.70  
  Purchase #7 $236.46   11.106%   $262.7212   $262.72   $262.70   $262.70  
  7 purchase totals = $649.66       $704.1033   $704.11   $704.05   $704.10