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	$60.37	6.783%	$64.4649	$64.46	$64.45	$64.50
Purchase #2	$82.95	10.834%	$91.9368	$91.94	$91.95	$91.90
Purchase #3	$46.71	11.616%	$52.1358	$52.14	$52.15	$52.10
Purchase #4	$19.31	11.109%	$21.4551	$21.46	$21.45	$21.50
Purchase #5	$105.29	12.565%	$118.5197	$118.52	$118.50	$118.50
Purchase #6	$8.74	9.736%	$9.5909	$9.59	$9.60	$9.60
Purchase #7	$169.78	10.815%	$188.1417	$188.14	$188.15	$188.10
7 purchase totals =	$493.15		$546.2449	$546.25	$546.25	$546.20