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	$154.63	3.525%	$160.0807	$160.08	$160.10	$160.10
Purchase #2	$98.66	13.686%	$112.1626	$112.16	$112.15	$112.20
Purchase #3	$75.86	3.860%	$78.7882	$78.79	$78.80	$78.80
Purchase #4	$184.46	3.820%	$191.5064	$191.51	$191.50	$191.50
Purchase #5	$158.25	9.542%	$173.3502	$173.35	$173.35	$173.40
Purchase #6	$54.37	10.316%	$59.9788	$59.98	$60.00	$60.00
Purchase #7	$195.37	11.740%	$218.3064	$218.31	$218.30	$218.30
7 purchase totals =	$921.60		$994.1733	$994.18	$994.20	$994.30