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	$31.79	6.414%	$33.829	$33.83	$33.85	$33.80
Purchase #2	$178.30	8.108%	$192.7566	$192.76	$192.75	$192.80
Purchase #3	$59.71	7.318%	$64.0796	$64.08	$64.10	$64.10
Purchase #4	$83.51	7.644%	$89.8935	$89.89	$89.90	$89.90
Purchase #5	$204.62	6.261%	$217.4313	$217.43	$217.45	$217.40
Purchase #6	$106.63	3.434%	$110.2917	$110.29	$110.30	$110.30
Purchase #7	$14.38	5.798%	$15.2138	$15.21	$15.20	$15.20
7 purchase totals =	$678.94		$723.4955	$723.49	$723.55	$723.50