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	$23.72	10.842%	$26.2917	$26.29	$26.30	$26.30
Purchase #2	$105.54	8.654%	$114.6734	$114.67	$114.65	$114.70
Purchase #3	$56.41	8.467%	$61.1862	$61.19	$61.20	$61.20
Purchase #4	$168.46	3.226%	$173.8945	$173.89	$173.90	$173.90
Purchase #5	$211.79	12.745%	$238.7826	$238.78	$238.80	$238.80
Purchase #6	$157.50	4.675%	$164.8631	$164.86	$164.85	$164.90
Purchase #7	$84.41	7.352%	$90.6158	$90.62	$90.60	$90.60
7 purchase totals =	$807.83		$870.3073	$870.30	$870.30	$870.40