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	$110.44	7.121%	$118.3044	$118.30	$118.30	$118.30
Purchase #2	$190.58	12.873%	$215.1134	$215.11	$215.10	$215.10
Purchase #3	$190.92	8.815%	$207.7496	$207.75	$207.75	$207.70
Purchase #4	$98.35	13.715%	$111.8387	$111.84	$111.85	$111.80
Purchase #5	$96.53	4.514%	$100.8874	$100.89	$100.90	$100.90
Purchase #6	$53.67	5.464%	$56.6025	$56.60	$56.60	$56.60
Purchase #7	$161.96	5.679%	$171.1577	$171.16	$171.15	$171.20
7 purchase totals =	$902.45		$981.6537	$981.65	$981.65	$981.60