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	$141.92	4.685%	$148.569	$148.57	$148.55	$148.60
Purchase #2	$160.28	11.219%	$178.2618	$178.26	$178.25	$178.30
Purchase #3	$116.39	6.439%	$123.8844	$123.88	$123.90	$123.90
Purchase #4	$127.51	13.454%	$144.6652	$144.67	$144.65	$144.70
Purchase #5	$158.82	13.274%	$179.9018	$179.90	$179.90	$179.90
Purchase #6	$36.38	11.637%	$40.6135	$40.61	$40.60	$40.60
Purchase #7	$17.41	12.317%	$19.5544	$19.55	$19.55	$19.60
7 purchase totals =	$758.71		$835.4501	$835.44	$835.40	$835.60