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	$71.69	9.183%	$78.2733	$78.27	$78.25	$78.30
Purchase #2	$26.63	10.212%	$29.3495	$29.35	$29.35	$29.30
Purchase #3	$165.53	10.653%	$183.1639	$183.16	$183.15	$183.20
Purchase #4	$50.66	10.201%	$55.8278	$55.83	$55.85	$55.80
Purchase #5	$39.79	3.693%	$41.2594	$41.26	$41.25	$41.30
Purchase #6	$248.75	12.682%	$280.2965	$280.30	$280.30	$280.30
Purchase #7	$124.32	13.741%	$141.4028	$141.40	$141.40	$141.40
7 purchase totals =	$727.37		$809.5732	$809.57	$809.55	$809.60