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 $248.29   6.164%   $263.5946   $263.59   $263.60   $263.60  
  Purchase #2 $225.68   4.451%   $235.725   $235.73   $235.75   $235.70  
  Purchase #3 $34.49   11.796%   $38.5584   $38.56   $38.55   $38.60  
  Purchase #4 $194.98   11.411%   $217.2292   $217.23   $217.25   $217.20  
  Purchase #5 $18.50   4.671%   $19.3641   $19.36   $19.35   $19.40  
  Purchase #6 $113.36   9.326%   $123.932   $123.93   $123.95   $123.90  
  Purchase #7 $133.69   13.650%   $151.9387   $151.94   $151.95   $151.90  
  7 purchase totals = $968.99       $1,050.3420   $1,050.34   $1,050.40   $1,050.30