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	$31.77	10.591%	$35.1348	$35.13	$35.15	$35.10
Purchase #2	$83.65	10.515%	$92.4458	$92.45	$92.45	$92.40
Purchase #3	$85.67	4.463%	$89.4935	$89.49	$89.50	$89.50
Purchase #4	$53.60	10.371%	$59.1589	$59.16	$59.15	$59.20
Purchase #5	$112.89	3.689%	$117.0545	$117.05	$117.05	$117.10
Purchase #6	$60.29	10.563%	$66.6584	$66.66	$66.65	$66.70
Purchase #7	$162.33	8.865%	$176.7206	$176.72	$176.70	$176.70
7 purchase totals =	$590.20		$636.6665	$636.66	$636.65	$636.70