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	$107.74	12.468%	$121.173	$121.17	$121.15	$121.20
Purchase #2	$61.28	6.569%	$65.3055	$65.31	$65.30	$65.30
Purchase #3	$32.28	8.743%	$35.1022	$35.10	$35.10	$35.10
Purchase #4	$133.85	6.696%	$142.8126	$142.81	$142.80	$142.80
Purchase #5	$208.87	6.400%	$222.2377	$222.24	$222.25	$222.20
Purchase #6	$87.77	3.364%	$90.7226	$90.72	$90.70	$90.70
Purchase #7	$154.86	4.808%	$162.3057	$162.31	$162.30	$162.30
7 purchase totals =	$786.65		$839.6593	$839.66	$839.60	$839.60