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	$169.49	10.340%	$187.0153	$187.02	$187.00	$187.00
Purchase #2	$250.25	13.672%	$284.4642	$284.46	$284.45	$284.50
Purchase #3	$229.89	12.467%	$258.5504	$258.55	$258.55	$258.60
Purchase #4	$106.88	4.336%	$111.5143	$111.51	$111.50	$111.50
Purchase #5	$239.83	12.113%	$268.8806	$268.88	$268.90	$268.90
Purchase #6	$170.78	12.846%	$192.7184	$192.72	$192.70	$192.70
Purchase #7	$243.25	12.509%	$273.6781	$273.68	$273.70	$273.70
7 purchase totals =	$1,410.37		$1,576.8213	$1,576.82	$1,576.80	$1,576.90