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	$180.73	4.200%	$188.3207	$188.32	$188.30	$188.30
Purchase #2	$15.62	9.137%	$17.0472	$17.05	$17.05	$17.00
Purchase #3	$67.73	6.562%	$72.1744	$72.17	$72.15	$72.20
Purchase #4	$172.65	13.840%	$196.5448	$196.54	$196.55	$196.50
Purchase #5	$250.56	9.565%	$274.5261	$274.53	$274.55	$274.50
Purchase #6	$18.43	5.860%	$19.51	$19.51	$19.50	$19.50
Purchase #7	$112.62	8.850%	$122.5869	$122.59	$122.60	$122.60
7 purchase totals =	$818.34		$890.7101	$890.71	$890.70	$890.60