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	$79.77	11.191%	$88.6971	$88.70	$88.70	$88.70
Purchase #2	$234.30	13.443%	$265.7969	$265.80	$265.80	$265.80
Purchase #3	$107.37	4.419%	$112.1147	$112.11	$112.10	$112.10
Purchase #4	$34.70	6.743%	$37.0398	$37.04	$37.05	$37.00
Purchase #5	$165.94	9.613%	$181.8918	$181.89	$181.90	$181.90
Purchase #6	$158.77	7.611%	$170.854	$170.85	$170.85	$170.90
Purchase #7	$31.54	12.471%	$35.4734	$35.47	$35.45	$35.50
7 purchase totals =	$812.39		$891.8677	$891.86	$891.85	$891.90