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	$230.92	11.207%	$256.7992	$256.80	$256.80	$256.80
Purchase #2	$67.59	5.250%	$71.1385	$71.14	$71.15	$71.10
Purchase #3	$145.88	4.187%	$151.988	$151.99	$152.00	$152.00
Purchase #4	$198.89	7.443%	$213.6934	$213.69	$213.70	$213.70
Purchase #5	$152.31	4.308%	$158.8715	$158.87	$158.85	$158.90
Purchase #6	$158.84	13.673%	$180.5582	$180.56	$180.55	$180.60
Purchase #7	$129.75	9.258%	$141.7623	$141.76	$141.75	$141.80
7 purchase totals =	$1,084.18		$1,174.8111	$1,174.81	$1,174.80	$1,174.90