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	$101.97	8.388%	$110.5232	$110.52	$110.50	$110.50
Purchase #2	$163.55	9.471%	$179.0398	$179.04	$179.05	$179.00
Purchase #3	$80.48	11.226%	$89.5147	$89.51	$89.50	$89.50
Purchase #4	$14.85	3.258%	$15.3338	$15.33	$15.35	$15.30
Purchase #5	$178.82	5.261%	$188.2277	$188.23	$188.25	$188.20
Purchase #6	$152.61	10.185%	$168.1533	$168.15	$168.15	$168.20
Purchase #7	$28.54	9.103%	$31.138	$31.14	$31.15	$31.10
7 purchase totals =	$720.82		$781.9305	$781.92	$781.95	$781.80