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	$249.62	8.102%	$269.8442	$269.84	$269.85	$269.80
Purchase #2	$168.60	13.321%	$191.0592	$191.06	$191.05	$191.10
Purchase #3	$35.68	5.362%	$37.5932	$37.59	$37.60	$37.60
Purchase #4	$174.88	3.372%	$180.777	$180.78	$180.80	$180.80
Purchase #5	$136.83	5.469%	$144.3132	$144.31	$144.30	$144.30
Purchase #6	$205.40	11.632%	$229.2921	$229.29	$229.30	$229.30
Purchase #7	$125.46	4.309%	$130.8661	$130.87	$130.85	$130.90
7 purchase totals =	$1,096.47		$1,183.7450	$1,183.74	$1,183.75	$1,183.80