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	$50.27	13.127%	$56.8689	$56.87	$56.85	$56.90
Purchase #2	$84.46	8.747%	$91.8477	$91.85	$91.85	$91.80
Purchase #3	$149.88	10.396%	$165.4615	$165.46	$165.45	$165.50
Purchase #4	$22.60	7.623%	$24.3228	$24.32	$24.30	$24.30
Purchase #5	$6.51	13.532%	$7.3909	$7.39	$7.40	$7.40
Purchase #6	$190.89	11.543%	$212.9244	$212.92	$212.90	$212.90
Purchase #7	$149.66	7.206%	$160.4445	$160.44	$160.45	$160.40
7 purchase totals =	$654.27		$719.2607	$719.25	$719.20	$719.20