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	$40.82	11.333%	$45.4461	$45.45	$45.45	$45.40
Purchase #2	$158.55	8.538%	$172.087	$172.09	$172.10	$172.10
Purchase #3	$31.69	12.757%	$35.7327	$35.73	$35.75	$35.70
Purchase #4	$81.79	9.842%	$89.8398	$89.84	$89.85	$89.80
Purchase #5	$109.39	10.334%	$120.6944	$120.69	$120.70	$120.70
Purchase #6	$118.27	11.784%	$132.2069	$132.21	$132.20	$132.20
Purchase #7	$183.61	10.643%	$203.1516	$203.15	$203.15	$203.20
7 purchase totals =	$724.12		$799.1585	$799.16	$799.20	$799.10