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	$109.91	12.481%	$123.6279	$123.63	$123.65	$123.60
Purchase #2	$196.58	11.182%	$218.5616	$218.56	$218.55	$218.60
Purchase #3	$154.81	7.115%	$165.8247	$165.82	$165.80	$165.80
Purchase #4	$46.74	11.385%	$52.0613	$52.06	$52.05	$52.10
Purchase #5	$167.80	13.734%	$190.8457	$190.85	$190.85	$190.80
Purchase #6	$173.84	7.454%	$186.798	$186.80	$186.80	$186.80
Purchase #7	$9.66	8.656%	$10.4962	$10.50	$10.50	$10.50
7 purchase totals =	$859.34		$948.2154	$948.22	$948.20	$948.20