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	$248.86	6.331%	$264.6153	$264.62	$264.60	$264.60
Purchase #2	$113.45	3.374%	$117.2778	$117.28	$117.30	$117.30
Purchase #3	$133.98	12.587%	$150.8441	$150.84	$150.85	$150.80
Purchase #4	$107.25	6.226%	$113.9274	$113.93	$113.95	$113.90
Purchase #5	$215.63	10.454%	$238.172	$238.17	$238.15	$238.20
Purchase #6	$187.54	9.125%	$204.653	$204.65	$204.65	$204.70
Purchase #7	$73.78	11.791%	$82.4794	$82.48	$82.50	$82.50
7 purchase totals =	$1,080.49		$1,171.9690	$1,171.97	$1,172.00	$1,172.00