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	$8.79	13.725%	$9.9964	$10.00	$10.00	$10.00
Purchase #2	$154.94	6.401%	$164.8577	$164.86	$164.85	$164.90
Purchase #3	$146.43	12.850%	$165.2463	$165.25	$165.25	$165.20
Purchase #4	$179.94	6.331%	$191.332	$191.33	$191.35	$191.30
Purchase #5	$16.94	4.551%	$17.7109	$17.71	$17.70	$17.70
Purchase #6	$39.77	6.374%	$42.3049	$42.30	$42.30	$42.30
Purchase #7	$83.28	7.695%	$89.6884	$89.69	$89.70	$89.70
7 purchase totals =	$630.09		$681.1366	$681.14	$681.15	$681.10