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	$180.70	10.689%	$200.015	$200.02	$200.00	$200.00
Purchase #2	$239.48	7.249%	$256.8399	$256.84	$256.85	$256.80
Purchase #3	$148.66	4.168%	$154.8561	$154.86	$154.85	$154.90
Purchase #4	$247.93	8.832%	$269.8272	$269.83	$269.85	$269.80
Purchase #5	$158.81	10.373%	$175.2834	$175.28	$175.30	$175.30
Purchase #6	$19.44	4.278%	$20.2716	$20.27	$20.25	$20.30
Purchase #7	$160.29	3.191%	$165.4049	$165.40	$165.40	$165.40
7 purchase totals =	$1,155.31		$1,242.4981	$1,242.50	$1,242.50	$1,242.50