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	$23.53	7.503%	$25.2955	$25.30	$25.30	$25.30
Purchase #2	$144.90	7.231%	$155.3777	$155.38	$155.40	$155.40
Purchase #3	$71.43	9.628%	$78.3073	$78.31	$78.30	$78.30
Purchase #4	$26.42	10.311%	$29.1442	$29.14	$29.15	$29.10
Purchase #5	$47.43	5.412%	$49.9969	$50.00	$50.00	$50.00
Purchase #6	$147.68	5.184%	$155.3357	$155.34	$155.35	$155.30
Purchase #7	$153.67	8.767%	$167.1422	$167.14	$167.15	$167.10
7 purchase totals =	$615.06		$660.5995	$660.61	$660.65	$660.50