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	$28.65	3.739%	$29.7212	$29.72	$29.70	$29.70
Purchase #2	$156.53	10.468%	$172.9156	$172.92	$172.90	$172.90
Purchase #3	$12.42	11.709%	$13.8743	$13.87	$13.85	$13.90
Purchase #4	$239.73	4.551%	$250.6401	$250.64	$250.65	$250.60
Purchase #5	$180.62	3.756%	$187.4041	$187.40	$187.40	$187.40
Purchase #6	$35.36	4.703%	$37.023	$37.02	$37.00	$37.00
Purchase #7	$128.33	3.508%	$132.8318	$132.83	$132.85	$132.80
7 purchase totals =	$781.64		$824.4101	$824.40	$824.35	$824.30