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	$11.30	7.874%	$12.1898	$12.19	$12.20	$12.20
Purchase #2	$90.49	10.146%	$99.6711	$99.67	$99.65	$99.70
Purchase #3	$64.92	11.119%	$72.1385	$72.14	$72.15	$72.10
Purchase #4	$77.69	5.123%	$81.6701	$81.67	$81.65	$81.70
Purchase #5	$125.76	4.296%	$131.1626	$131.16	$131.15	$131.20
Purchase #6	$208.73	12.140%	$234.0698	$234.07	$234.05	$234.10
Purchase #7	$212.39	5.821%	$224.7532	$224.75	$224.75	$224.80
7 purchase totals =	$791.28		$855.6551	$855.65	$855.60	$855.80