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	$5.34	4.685%	$5.5902	$5.59	$5.60	$5.60
Purchase #2	$51.41	3.872%	$53.4006	$53.40	$53.40	$53.40
Purchase #3	$20.78	7.367%	$22.3109	$22.31	$22.30	$22.30
Purchase #4	$30.82	5.350%	$32.4689	$32.47	$32.45	$32.50
Purchase #5	$103.30	12.350%	$116.0576	$116.06	$116.05	$116.10
Purchase #6	$89.62	12.424%	$100.7544	$100.75	$100.75	$100.80
Purchase #7	$64.69	13.272%	$73.2757	$73.28	$73.30	$73.30
7 purchase totals =	$365.96		$403.8583	$403.86	$403.85	$404.00