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	$64.93	10.130%	$71.5074	$71.51	$71.50	$71.50
Purchase #2	$55.57	9.289%	$60.7319	$60.73	$60.75	$60.70
Purchase #3	$101.59	9.313%	$111.0511	$111.05	$111.05	$111.10
Purchase #4	$203.43	6.108%	$215.8555	$215.86	$215.85	$215.90
Purchase #5	$35.75	6.494%	$38.0716	$38.07	$38.05	$38.10
Purchase #6	$9.35	11.679%	$10.442	$10.44	$10.45	$10.40
Purchase #7	$81.40	8.293%	$88.1505	$88.15	$88.15	$88.20
7 purchase totals =	$552.02		$595.8100	$595.81	$595.80	$595.90