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	$183.78	13.345%	$208.3054	$208.31	$208.30	$208.30
Purchase #2	$156.25	3.783%	$162.1609	$162.16	$162.15	$162.20
Purchase #3	$195.98	11.772%	$219.0508	$219.05	$219.05	$219.10
Purchase #4	$153.31	10.398%	$169.2512	$169.25	$169.25	$169.30
Purchase #5	$55.61	12.588%	$62.6102	$62.61	$62.60	$62.60
Purchase #6	$79.47	12.814%	$89.6533	$89.65	$89.65	$89.70
Purchase #7	$220.67	13.169%	$249.73	$249.73	$249.75	$249.70
7 purchase totals =	$1,045.07		$1,160.7618	$1,160.76	$1,160.75	$1,160.90