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	$164.43	12.140%	$184.3918	$184.39	$184.40	$184.40
Purchase #2	$199.58	10.274%	$220.0848	$220.08	$220.10	$220.10
Purchase #3	$189.91	9.666%	$208.2667	$208.27	$208.25	$208.30
Purchase #4	$95.39	8.360%	$103.3646	$103.36	$103.35	$103.40
Purchase #5	$107.33	10.385%	$118.4762	$118.48	$118.50	$118.50
Purchase #6	$204.81	8.499%	$222.2168	$222.22	$222.20	$222.20
Purchase #7	$155.93	6.112%	$165.4604	$165.46	$165.45	$165.50
7 purchase totals =	$1,117.38		$1,222.2613	$1,222.26	$1,222.25	$1,222.40