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	$30.64	5.431%	$32.3041	$32.30	$32.30	$32.30
Purchase #2	$103.26	13.679%	$117.3849	$117.38	$117.40	$117.40
Purchase #3	$50.57	9.167%	$55.2058	$55.21	$55.20	$55.20
Purchase #4	$214.33	6.303%	$227.8392	$227.84	$227.85	$227.80
Purchase #5	$72.64	13.263%	$82.2742	$82.27	$82.25	$82.30
Purchase #6	$165.76	13.548%	$188.2172	$188.22	$188.20	$188.20
Purchase #7	$99.98	7.627%	$107.6055	$107.61	$107.60	$107.60
7 purchase totals =	$737.18		$810.8309	$810.83	$810.80	$810.80