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	$108.66	12.800%	$122.5685	$122.57	$122.55	$122.60
Purchase #2	$56.31	10.401%	$62.1668	$62.17	$62.15	$62.20
Purchase #3	$73.52	12.269%	$82.5402	$82.54	$82.55	$82.50
Purchase #4	$81.31	11.602%	$90.7436	$90.74	$90.75	$90.70
Purchase #5	$139.52	10.543%	$154.2296	$154.23	$154.25	$154.20
Purchase #6	$54.95	13.193%	$62.1996	$62.20	$62.20	$62.20
Purchase #7	$209.54	13.722%	$238.2931	$238.29	$238.30	$238.30
7 purchase totals =	$723.81		$812.7414	$812.74	$812.75	$812.70