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	$201.73	13.156%	$228.2696	$228.27	$228.25	$228.30
Purchase #2	$146.56	8.136%	$158.4841	$158.48	$158.50	$158.50
Purchase #3	$107.84	4.137%	$112.3013	$112.30	$112.30	$112.30
Purchase #4	$229.59	8.250%	$248.5312	$248.53	$248.55	$248.50
Purchase #5	$33.82	9.466%	$37.0214	$37.02	$37.00	$37.00
Purchase #6	$31.43	12.768%	$35.443	$35.44	$35.45	$35.40
Purchase #7	$65.75	7.581%	$70.7345	$70.73	$70.75	$70.70
7 purchase totals =	$816.72		$890.7851	$890.77	$890.80	$890.70