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	$159.95	12.183%	$179.4367	$179.44	$179.45	$179.40
Purchase #2	$52.68	12.509%	$59.2697	$59.27	$59.25	$59.30
Purchase #3	$149.46	8.760%	$162.5527	$162.55	$162.55	$162.60
Purchase #4	$143.55	9.137%	$156.6662	$156.67	$156.65	$156.70
Purchase #5	$62.74	7.606%	$67.512	$67.51	$67.50	$67.50
Purchase #6	$162.63	5.600%	$171.7373	$171.74	$171.75	$171.70
Purchase #7	$143.87	11.130%	$159.8827	$159.88	$159.90	$159.90
7 purchase totals =	$874.88		$957.0573	$957.06	$957.05	$957.10