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	$50.81	4.666%	$53.1808	$53.18	$53.20	$53.20
Purchase #2	$184.51	11.520%	$205.7656	$205.77	$205.75	$205.80
Purchase #3	$85.81	4.795%	$89.9246	$89.92	$89.90	$89.90
Purchase #4	$81.86	12.428%	$92.0336	$92.03	$92.05	$92.00
Purchase #5	$64.64	12.392%	$72.6502	$72.65	$72.65	$72.70
Purchase #6	$235.27	11.461%	$262.2343	$262.23	$262.25	$262.20
Purchase #7	$63.57	11.643%	$70.9715	$70.97	$70.95	$71.00
7 purchase totals =	$766.47		$846.7606	$846.75	$846.75	$846.80