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	$173.33	4.160%	$180.5405	$180.54	$180.55	$180.50
Purchase #2	$53.28	11.829%	$59.5825	$59.58	$59.60	$59.60
Purchase #3	$99.61	12.506%	$112.0672	$112.07	$112.05	$112.10
Purchase #4	$106.39	12.235%	$119.4068	$119.41	$119.40	$119.40
Purchase #5	$63.71	11.227%	$70.8627	$70.86	$70.85	$70.90
Purchase #6	$239.69	3.594%	$248.3045	$248.30	$248.30	$248.30
Purchase #7	$187.59	6.571%	$199.9165	$199.92	$199.90	$199.90
7 purchase totals =	$923.60		$990.6807	$990.68	$990.65	$990.70