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	$162.81	4.592%	$170.2862	$170.29	$170.30	$170.30
Purchase #2	$86.89	3.312%	$89.7678	$89.77	$89.75	$89.80
Purchase #3	$71.98	13.640%	$81.7981	$81.80	$81.80	$81.80
Purchase #4	$207.32	13.780%	$235.8887	$235.89	$235.90	$235.90
Purchase #5	$240.99	11.325%	$268.2821	$268.28	$268.30	$268.30
Purchase #6	$41.61	10.167%	$45.8405	$45.84	$45.85	$45.80
Purchase #7	$190.92	7.313%	$204.882	$204.88	$204.90	$204.90
7 purchase totals =	$1,002.52		$1,096.7454	$1,096.75	$1,096.80	$1,096.80