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	$60.91	12.119%	$68.2917	$68.29	$68.30	$68.30
Purchase #2	$239.42	6.540%	$255.0781	$255.08	$255.10	$255.10
Purchase #3	$100.40	9.133%	$109.5695	$109.57	$109.55	$109.60
Purchase #4	$143.55	5.109%	$150.884	$150.88	$150.90	$150.90
Purchase #5	$165.40	10.557%	$182.8613	$182.86	$182.85	$182.90
Purchase #6	$16.92	13.595%	$19.2203	$19.22	$19.20	$19.20
Purchase #7	$67.82	3.402%	$70.1272	$70.13	$70.15	$70.10
7 purchase totals =	$794.42		$856.0321	$856.03	$856.05	$856.10