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 $90.32   6.298%   $96.0084   $96.01   $96.00   $96.00  
  Purchase #2 $124.27   3.265%   $128.3274   $128.33   $128.35   $128.30  
  Purchase #3 $101.91   11.471%   $113.6001   $113.60   $113.60   $113.60  
  Purchase #4 $250.81   11.694%   $280.1397   $280.14   $280.15   $280.10  
  Purchase #5 $63.93   6.840%   $68.3028   $68.30   $68.30   $68.30  
  Purchase #6 $182.31   13.105%   $206.2017   $206.20   $206.20   $206.20  
  Purchase #7 $192.89   10.728%   $213.5832   $213.58   $213.60   $213.60  
  7 purchase totals = $1,006.44       $1,106.1633   $1,106.16   $1,106.20   $1,106.10