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 $190.59   11.864%   $213.2016   $213.20   $213.20   $213.20  
  Purchase #2 $177.75   6.249%   $188.8576   $188.86   $188.85   $188.90  
  Purchase #3 $98.54   9.118%   $107.5249   $107.52   $107.50   $107.50  
  Purchase #4 $123.63   12.629%   $139.2432   $139.24   $139.25   $139.20  
  Purchase #5 $161.66   10.581%   $178.7652   $178.77   $178.75   $178.80  
  Purchase #6 $19.62   5.153%   $20.631   $20.63   $20.65   $20.60  
  Purchase #7 $185.91   11.430%   $207.1595   $207.16   $207.15   $207.20  
  7 purchase totals = $957.70       $1,055.3830   $1,055.38   $1,055.35   $1,055.40