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	$161.49	4.330%	$168.4825	$168.48	$168.50	$168.50
Purchase #2	$135.37	13.606%	$153.7884	$153.79	$153.80	$153.80
Purchase #3	$169.73	10.482%	$187.5211	$187.52	$187.50	$187.50
Purchase #4	$223.78	4.839%	$234.6087	$234.61	$234.60	$234.60
Purchase #5	$93.82	4.130%	$97.6948	$97.69	$97.70	$97.70
Purchase #6	$110.88	13.861%	$126.2491	$126.25	$126.25	$126.20
Purchase #7	$185.68	4.761%	$194.5202	$194.52	$194.50	$194.50
7 purchase totals =	$1,080.75		$1,162.8648	$1,162.86	$1,162.85	$1,162.80