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	$139.61	8.361%	$151.2828	$151.28	$151.30	$151.30
Purchase #2	$141.86	9.607%	$155.4885	$155.49	$155.50	$155.50
Purchase #3	$159.36	5.107%	$167.4985	$167.50	$167.50	$167.50
Purchase #4	$75.35	13.117%	$85.2337	$85.23	$85.25	$85.20
Purchase #5	$98.83	13.614%	$112.2847	$112.28	$112.30	$112.30
Purchase #6	$55.50	3.325%	$57.3454	$57.35	$57.35	$57.30
Purchase #7	$182.68	4.177%	$190.3105	$190.31	$190.30	$190.30
7 purchase totals =	$853.19		$919.4441	$919.44	$919.50	$919.40