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	$107.93	9.745%	$118.4478	$118.45	$118.45	$118.40
Purchase #2	$89.91	4.860%	$94.2796	$94.28	$94.30	$94.30
Purchase #3	$196.28	6.112%	$208.2766	$208.28	$208.30	$208.30
Purchase #4	$157.74	4.734%	$165.2074	$165.21	$165.20	$165.20
Purchase #5	$10.89	3.346%	$11.2544	$11.25	$11.25	$11.30
Purchase #6	$79.33	4.870%	$83.1934	$83.19	$83.20	$83.20
Purchase #7	$167.92	12.842%	$189.4843	$189.48	$189.50	$189.50
7 purchase totals =	$810.00		$870.1435	$870.14	$870.20	$870.20