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	$96.49	6.796%	$103.0475	$103.05	$103.05	$103.00
Purchase #2	$24.94	13.819%	$28.3865	$28.39	$28.40	$28.40
Purchase #3	$215.41	11.674%	$240.557	$240.56	$240.55	$240.60
Purchase #4	$249.26	10.559%	$275.5794	$275.58	$275.60	$275.60
Purchase #5	$210.82	12.158%	$236.4515	$236.45	$236.45	$236.50
Purchase #6	$32.38	10.429%	$35.7569	$35.76	$35.75	$35.80
Purchase #7	$163.83	13.210%	$185.4719	$185.47	$185.45	$185.50
7 purchase totals =	$993.13		$1,105.2507	$1,105.26	$1,105.25	$1,105.40