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	$57.44	5.359%	$60.5182	$60.52	$60.50	$60.50
Purchase #2	$242.27	9.638%	$265.62	$265.62	$265.60	$265.60
Purchase #3	$90.28	10.440%	$99.7052	$99.71	$99.70	$99.70
Purchase #4	$142.55	3.416%	$147.4195	$147.42	$147.40	$147.40
Purchase #5	$155.27	5.815%	$164.299	$164.30	$164.30	$164.30
Purchase #6	$106.61	13.321%	$120.8115	$120.81	$120.80	$120.80
Purchase #7	$216.84	11.665%	$242.1344	$242.13	$242.15	$242.10
7 purchase totals =	$1,011.26		$1,100.5078	$1,100.51	$1,100.45	$1,100.40