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 $88.25   8.790%   $96.0072   $96.01   $96.00   $96.00  
  Purchase #2 $136.41   4.586%   $142.6658   $142.67   $142.65   $142.70  
  Purchase #3 $234.46   11.266%   $260.8743   $260.87   $260.85   $260.90  
  Purchase #4 $188.30   9.845%   $206.8381   $206.84   $206.85   $206.80  
  Purchase #5 $18.93   11.411%   $21.0901   $21.09   $21.10   $21.10  
  Purchase #6 $83.33   3.410%   $86.1716   $86.17   $86.15   $86.20  
  Purchase #7 $169.36   10.659%   $187.4121   $187.41   $187.40   $187.40  
  7 purchase totals = $919.04       $1,001.0592   $1,001.06   $1,001.00   $1,001.10