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 $205.58   4.671%   $215.1826   $215.18   $215.20   $215.20  
  Purchase #2 $54.63   12.516%   $61.4675   $61.47   $61.45   $61.50  
  Purchase #3 $196.52   4.564%   $205.4892   $205.49   $205.50   $205.50  
  Purchase #4 $185.91   11.313%   $206.942   $206.94   $206.95   $206.90  
  Purchase #5 $206.95   6.546%   $220.4969   $220.50   $220.50   $220.50  
  Purchase #6 $13.68   8.114%   $14.79   $14.79   $14.80   $14.80  
  Purchase #7 $43.51   3.115%   $44.8653   $44.87   $44.85   $44.90  
  7 purchase totals = $906.78       $969.2335   $969.24   $969.25   $969.30