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 $77.74   11.740%   $86.8667   $86.87   $86.85   $86.90  
  Purchase #2 $237.39   10.621%   $262.6032   $262.60   $262.60   $262.60  
  Purchase #3 $124.78   7.594%   $134.2558   $134.26   $134.25   $134.30  
  Purchase #4 $109.51   13.189%   $123.9533   $123.95   $123.95   $124.00  
  Purchase #5 $191.83   10.623%   $212.2081   $212.21   $212.20   $212.20  
  Purchase #6 $14.26   7.370%   $15.311   $15.31   $15.30   $15.30  
  Purchase #7 $76.83   9.111%   $83.83   $83.83   $83.85   $83.80  
  7 purchase totals = $832.34       $919.0281   $919.03   $919.00   $919.10