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	$52.30	12.857%	$59.0242	$59.02	$59.00	$59.00
Purchase #2	$199.30	6.788%	$212.8285	$212.83	$212.85	$212.80
Purchase #3	$122.90	3.757%	$127.5174	$127.52	$127.50	$127.50
Purchase #4	$175.86	13.606%	$199.7875	$199.79	$199.80	$199.80
Purchase #5	$17.63	3.581%	$18.2613	$18.26	$18.25	$18.30
Purchase #6	$210.59	6.671%	$224.6385	$224.64	$224.65	$224.60
Purchase #7	$191.53	3.820%	$198.8464	$198.85	$198.85	$198.80
7 purchase totals =	$970.11		$1,040.9038	$1,040.91	$1,040.90	$1,040.80