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	$30.78	4.373%	$32.126	$32.13	$32.15	$32.10
Purchase #2	$139.71	6.547%	$148.8568	$148.86	$148.85	$148.90
Purchase #3	$35.68	3.736%	$37.013	$37.01	$37.00	$37.00
Purchase #4	$242.88	4.286%	$253.2898	$253.29	$253.30	$253.30
Purchase #5	$54.41	7.164%	$58.3079	$58.31	$58.30	$58.30
Purchase #6	$239.86	13.153%	$271.4088	$271.41	$271.40	$271.40
Purchase #7	$234.93	6.307%	$249.747	$249.75	$249.75	$249.70
7 purchase totals =	$978.25		$1,050.7493	$1,050.76	$1,050.75	$1,050.70