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	$136.38	8.568%	$148.065	$148.07	$148.05	$148.10
Purchase #2	$118.67	8.340%	$128.5671	$128.57	$128.55	$128.60
Purchase #3	$102.96	8.291%	$111.4964	$111.50	$111.50	$111.50
Purchase #4	$124.32	5.457%	$131.1041	$131.10	$131.10	$131.10
Purchase #5	$8.51	9.435%	$9.3129	$9.31	$9.30	$9.30
Purchase #6	$23.75	6.567%	$25.3097	$25.31	$25.30	$25.30
Purchase #7	$107.83	4.185%	$112.3427	$112.34	$112.35	$112.30
7 purchase totals =	$622.42		$666.1979	$666.20	$666.15	$666.20