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	$98.71	13.271%	$111.8098	$111.81	$111.80	$111.80
Purchase #2	$80.43	10.581%	$88.9403	$88.94	$88.95	$88.90
Purchase #3	$188.61	11.488%	$210.2775	$210.28	$210.30	$210.30
Purchase #4	$86.99	13.447%	$98.6875	$98.69	$98.70	$98.70
Purchase #5	$120.35	6.466%	$128.1318	$128.13	$128.15	$128.10
Purchase #6	$119.52	7.550%	$128.5438	$128.54	$128.55	$128.50
Purchase #7	$44.40	9.300%	$48.5292	$48.53	$48.55	$48.50
7 purchase totals =	$739.01		$814.9199	$814.92	$815.00	$814.80