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	$159.74	12.680%	$179.995	$180.00	$180.00	$180.00
Purchase #2	$175.94	3.211%	$181.5894	$181.59	$181.60	$181.60
Purchase #3	$131.61	7.739%	$141.7953	$141.80	$141.80	$141.80
Purchase #4	$32.43	3.739%	$33.6426	$33.64	$33.65	$33.60
Purchase #5	$39.33	13.852%	$44.778	$44.78	$44.80	$44.80
Purchase #6	$151.54	11.244%	$168.5792	$168.58	$168.60	$168.60
Purchase #7	$38.98	6.828%	$41.6416	$41.64	$41.65	$41.60
7 purchase totals =	$729.57		$792.0211	$792.03	$792.10	$792.00