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	$245.47	12.277%	$275.6064	$275.61	$275.60	$275.60
Purchase #2	$39.94	4.675%	$41.8072	$41.81	$41.80	$41.80
Purchase #3	$204.43	12.354%	$229.6853	$229.69	$229.70	$229.70
Purchase #4	$228.82	11.865%	$255.9695	$255.97	$255.95	$256.00
Purchase #5	$164.31	6.201%	$174.4989	$174.50	$174.50	$174.50
Purchase #6	$180.88	8.766%	$196.7359	$196.74	$196.75	$196.70
Purchase #7	$187.98	8.795%	$204.5128	$204.51	$204.50	$204.50
7 purchase totals =	$1,251.83		$1,378.8160	$1,378.83	$1,378.80	$1,378.80