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	$53.60	3.134%	$55.2798	$55.28	$55.30	$55.30
Purchase #2	$160.31	11.465%	$178.6895	$178.69	$178.70	$178.70
Purchase #3	$92.40	13.683%	$105.0431	$105.04	$105.05	$105.00
Purchase #4	$42.29	10.817%	$46.8645	$46.86	$46.85	$46.90
Purchase #5	$157.91	13.379%	$179.0368	$179.04	$179.05	$179.00
Purchase #6	$40.88	10.760%	$45.2787	$45.28	$45.30	$45.30
Purchase #7	$60.97	12.380%	$68.5181	$68.52	$68.50	$68.50
7 purchase totals =	$608.36		$678.7105	$678.71	$678.75	$678.70