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	$126.45	11.826%	$141.404	$141.40	$141.40	$141.40
Purchase #2	$90.29	10.222%	$99.5194	$99.52	$99.50	$99.50
Purchase #3	$94.46	5.320%	$99.4853	$99.49	$99.50	$99.50
Purchase #4	$158.90	11.358%	$176.9479	$176.95	$176.95	$176.90
Purchase #5	$228.59	7.614%	$245.9948	$245.99	$246.00	$246.00
Purchase #6	$83.62	7.336%	$89.7544	$89.75	$89.75	$89.80
Purchase #7	$53.98	6.137%	$57.2928	$57.29	$57.30	$57.30
7 purchase totals =	$836.29		$910.3986	$910.39	$910.40	$910.40