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	$133.40	5.862%	$141.2199	$141.22	$141.20	$141.20
Purchase #2	$123.83	3.508%	$128.174	$128.17	$128.15	$128.20
Purchase #3	$26.46	10.130%	$29.1404	$29.14	$29.15	$29.10
Purchase #4	$81.54	9.847%	$89.5692	$89.57	$89.55	$89.60
Purchase #5	$228.54	11.280%	$254.3193	$254.32	$254.30	$254.30
Purchase #6	$91.64	6.153%	$97.2786	$97.28	$97.30	$97.30
Purchase #7	$54.83	5.103%	$57.628	$57.63	$57.65	$57.60
7 purchase totals =	$740.24		$797.3294	$797.33	$797.30	$797.30