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	$130.37	11.627%	$145.5281	$145.53	$145.55	$145.50
Purchase #2	$83.62	8.584%	$90.7979	$90.80	$90.80	$90.80
Purchase #3	$191.53	7.855%	$206.5747	$206.57	$206.55	$206.60
Purchase #4	$170.69	12.111%	$191.3623	$191.36	$191.35	$191.40
Purchase #5	$93.52	5.291%	$98.4681	$98.47	$98.45	$98.50
Purchase #6	$200.57	4.343%	$209.2808	$209.28	$209.30	$209.30
Purchase #7	$54.44	3.807%	$56.5125	$56.51	$56.50	$56.50
7 purchase totals =	$924.74		$998.5244	$998.52	$998.50	$998.60