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	$78.86	6.128%	$83.6925	$83.69	$83.70	$83.70
Purchase #2	$26.52	8.419%	$28.7527	$28.75	$28.75	$28.80
Purchase #3	$133.35	9.668%	$146.2423	$146.24	$146.25	$146.20
Purchase #4	$165.95	11.673%	$185.3213	$185.32	$185.30	$185.30
Purchase #5	$126.97	9.713%	$139.3026	$139.30	$139.30	$139.30
Purchase #6	$242.82	5.179%	$255.3956	$255.40	$255.40	$255.40
Purchase #7	$111.77	11.570%	$124.7018	$124.70	$124.70	$124.70
7 purchase totals =	$886.24		$963.4088	$963.40	$963.40	$963.40