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	$167.33	6.830%	$178.7586	$178.76	$178.75	$178.80
Purchase #2	$230.44	4.229%	$240.1853	$240.19	$240.20	$240.20
Purchase #3	$124.37	4.393%	$129.8336	$129.83	$129.85	$129.80
Purchase #4	$52.89	13.103%	$59.8202	$59.82	$59.80	$59.80
Purchase #5	$124.97	3.109%	$128.8553	$128.86	$128.85	$128.90
Purchase #6	$132.75	8.839%	$144.4838	$144.48	$144.50	$144.50
Purchase #7	$235.80	12.738%	$265.8362	$265.84	$265.85	$265.80
7 purchase totals =	$1,068.55		$1,147.7730	$1,147.78	$1,147.80	$1,147.80