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	$30.98	4.163%	$32.2697	$32.27	$32.25	$32.30
Purchase #2	$149.40	7.277%	$160.2718	$160.27	$160.25	$160.30
Purchase #3	$216.39	6.146%	$229.6893	$229.69	$229.70	$229.70
Purchase #4	$67.50	5.206%	$71.0141	$71.01	$71.00	$71.00
Purchase #5	$60.38	13.512%	$68.5385	$68.54	$68.55	$68.50
Purchase #6	$30.52	9.849%	$33.5259	$33.53	$33.55	$33.50
Purchase #7	$207.97	13.274%	$235.5759	$235.58	$235.60	$235.60
7 purchase totals =	$763.14		$830.8852	$830.89	$830.90	$830.90