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	$147.50	4.525%	$154.1744	$154.17	$154.15	$154.20
Purchase #2	$73.35	11.471%	$81.764	$81.76	$81.75	$81.80
Purchase #3	$95.32	4.795%	$99.8906	$99.89	$99.90	$99.90
Purchase #4	$32.31	9.242%	$35.2961	$35.30	$35.30	$35.30
Purchase #5	$167.60	11.251%	$186.4567	$186.46	$186.45	$186.50
Purchase #6	$204.29	5.426%	$215.3748	$215.37	$215.35	$215.40
Purchase #7	$59.65	11.607%	$66.5736	$66.57	$66.55	$66.60
7 purchase totals =	$780.02		$839.5302	$839.52	$839.45	$839.70