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	$99.88	9.367%	$109.2358	$109.24	$109.25	$109.20
Purchase #2	$19.39	10.855%	$21.4948	$21.49	$21.50	$21.50
Purchase #3	$99.92	5.283%	$105.1988	$105.20	$105.20	$105.20
Purchase #4	$240.79	12.262%	$270.3157	$270.32	$270.30	$270.30
Purchase #5	$165.42	7.816%	$178.3492	$178.35	$178.35	$178.30
Purchase #6	$92.70	8.601%	$100.6731	$100.67	$100.65	$100.70
Purchase #7	$51.87	12.429%	$58.3169	$58.32	$58.30	$58.30
7 purchase totals =	$769.97		$843.5843	$843.59	$843.55	$843.50