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	$132.77	11.572%	$148.1341	$148.13	$148.15	$148.10
Purchase #2	$26.69	9.209%	$29.1479	$29.15	$29.15	$29.10
Purchase #3	$85.40	6.507%	$90.957	$90.96	$90.95	$91.00
Purchase #4	$118.97	6.363%	$126.5401	$126.54	$126.55	$126.50
Purchase #5	$79.74	12.301%	$89.5488	$89.55	$89.55	$89.50
Purchase #6	$31.98	11.637%	$35.7015	$35.70	$35.70	$35.70
Purchase #7	$83.52	11.193%	$92.8684	$92.87	$92.85	$92.90
7 purchase totals =	$559.07		$612.8978	$612.90	$612.90	$612.80