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	$29.79	11.658%	$33.2629	$33.26	$33.25	$33.30
Purchase #2	$232.88	5.457%	$245.5883	$245.59	$245.60	$245.60
Purchase #3	$33.79	13.583%	$38.3797	$38.38	$38.40	$38.40
Purchase #4	$72.56	7.677%	$78.1304	$78.13	$78.15	$78.10
Purchase #5	$242.75	10.630%	$268.5543	$268.55	$268.55	$268.60
Purchase #6	$137.72	6.359%	$146.4776	$146.48	$146.50	$146.50
Purchase #7	$54.64	10.346%	$60.2931	$60.29	$60.30	$60.30
7 purchase totals =	$804.13		$870.6863	$870.68	$870.75	$870.80