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	$78.87	3.160%	$81.3623	$81.36	$81.35	$81.40
Purchase #2	$35.28	7.427%	$37.9002	$37.90	$37.90	$37.90
Purchase #3	$50.78	11.826%	$56.7852	$56.79	$56.80	$56.80
Purchase #4	$154.41	11.236%	$171.7595	$171.76	$171.75	$171.80
Purchase #5	$111.26	6.597%	$118.5998	$118.60	$118.60	$118.60
Purchase #6	$180.61	6.189%	$191.788	$191.79	$191.80	$191.80
Purchase #7	$122.71	6.336%	$130.4849	$130.48	$130.50	$130.50
7 purchase totals =	$733.92		$788.6799	$788.68	$788.70	$788.80