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	$85.71	7.167%	$91.8528	$91.85	$91.85	$91.90
Purchase #2	$100.57	10.727%	$111.3581	$111.36	$111.35	$111.40
Purchase #3	$54.51	8.367%	$59.0709	$59.07	$59.05	$59.10
Purchase #4	$189.92	4.459%	$198.3885	$198.39	$198.40	$198.40
Purchase #5	$18.30	11.791%	$20.4578	$20.46	$20.45	$20.50
Purchase #6	$156.77	5.846%	$165.9348	$165.93	$165.95	$165.90
Purchase #7	$30.92	8.450%	$33.5327	$33.53	$33.55	$33.50
7 purchase totals =	$636.70		$680.5956	$680.59	$680.60	$680.70