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	$151.61	12.841%	$171.0782	$171.08	$171.10	$171.10
Purchase #2	$81.38	10.276%	$89.7426	$89.74	$89.75	$89.70
Purchase #3	$19.58	7.696%	$21.0869	$21.09	$21.10	$21.10
Purchase #4	$154.81	3.216%	$159.7887	$159.79	$159.80	$159.80
Purchase #5	$45.48	4.338%	$47.4529	$47.45	$47.45	$47.50
Purchase #6	$37.35	4.216%	$38.9247	$38.92	$38.90	$38.90
Purchase #7	$248.54	11.377%	$276.8164	$276.82	$276.80	$276.80
7 purchase totals =	$738.75		$804.8904	$804.89	$804.90	$804.90