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	$11.93	4.476%	$12.464	$12.46	$12.45	$12.50
Purchase #2	$98.27	9.513%	$107.6184	$107.62	$107.60	$107.60
Purchase #3	$93.61	5.610%	$98.8615	$98.86	$98.85	$98.90
Purchase #4	$31.54	12.391%	$35.4481	$35.45	$35.45	$35.40
Purchase #5	$130.35	13.408%	$147.8273	$147.83	$147.85	$147.80
Purchase #6	$238.61	4.308%	$248.8893	$248.89	$248.90	$248.90
Purchase #7	$139.34	4.113%	$145.0711	$145.07	$145.05	$145.10
7 purchase totals =	$743.65		$796.1797	$796.18	$796.15	$796.20