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	$107.57	3.443%	$111.2736	$111.27	$111.25	$111.30
Purchase #2	$222.71	11.787%	$248.9608	$248.96	$248.95	$249.00
Purchase #3	$51.35	8.230%	$55.5761	$55.58	$55.60	$55.60
Purchase #4	$111.65	11.587%	$124.5869	$124.59	$124.60	$124.60
Purchase #5	$133.66	11.388%	$148.8812	$148.88	$148.90	$148.90
Purchase #6	$83.77	7.776%	$90.284	$90.28	$90.30	$90.30
Purchase #7	$25.84	13.569%	$29.3462	$29.35	$29.35	$29.30
7 purchase totals =	$736.55		$808.9088	$808.91	$808.95	$809.00