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 $227.71   10.708%   $252.0932   $252.09   $252.10   $252.10  
  Purchase #2 $66.42   7.505%   $71.4048   $71.40   $71.40   $71.40  
  Purchase #3 $46.80   11.613%   $52.2349   $52.23   $52.25   $52.20  
  Purchase #4 $117.34   6.272%   $124.6996   $124.70   $124.70   $124.70  
  Purchase #5 $248.77   4.766%   $260.6264   $260.63   $260.65   $260.60  
  Purchase #6 $206.40   9.216%   $225.4218   $225.42   $225.40   $225.40  
  Purchase #7 $93.71   3.356%   $96.8549   $96.85   $96.85   $96.90  
  7 purchase totals = $1,007.15       $1,083.3356   $1,083.32   $1,083.35   $1,083.30