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 $123.88   12.304%   $139.1222   $139.12   $139.10   $139.10  
  Purchase #2 $219.69   7.358%   $235.8548   $235.85   $235.85   $235.90  
  Purchase #3 $50.52   7.787%   $54.454   $54.45   $54.45   $54.50  
  Purchase #4 $186.71   10.318%   $205.9747   $205.97   $205.95   $206.00  
  Purchase #5 $130.35   5.206%   $137.136   $137.14   $137.15   $137.10  
  Purchase #6 $82.45   5.436%   $86.932   $86.93   $86.95   $86.90  
  Purchase #7 $20.38   12.207%   $22.8678   $22.87   $22.85   $22.90  
  7 purchase totals = $813.98       $882.3415   $882.33   $882.30   $882.40