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	$40.26	12.838%	$45.4286	$45.43	$45.45	$45.40
Purchase #2	$91.73	7.471%	$98.5831	$98.58	$98.60	$98.60
Purchase #3	$50.37	6.692%	$53.7408	$53.74	$53.75	$53.70
Purchase #4	$73.37	10.250%	$80.8904	$80.89	$80.90	$80.90
Purchase #5	$151.46	9.417%	$165.723	$165.72	$165.70	$165.70
Purchase #6	$57.76	4.529%	$60.376	$60.38	$60.40	$60.40
Purchase #7	$71.88	8.744%	$78.1652	$78.17	$78.15	$78.20
7 purchase totals =	$536.83		$582.9071	$582.91	$582.95	$582.90