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	$40.63	3.301%	$41.9712	$41.97	$41.95	$42.00
Purchase #2	$114.31	11.617%	$127.5894	$127.59	$127.60	$127.60
Purchase #3	$20.87	12.125%	$23.4005	$23.40	$23.40	$23.40
Purchase #4	$136.77	12.667%	$154.0947	$154.09	$154.10	$154.10
Purchase #5	$90.84	9.723%	$99.6724	$99.67	$99.65	$99.70
Purchase #6	$161.62	11.338%	$179.9445	$179.94	$179.95	$179.90
Purchase #7	$187.33	6.710%	$199.8998	$199.90	$199.90	$199.90
7 purchase totals =	$752.37		$826.5725	$826.56	$826.55	$826.60