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	$231.86	4.627%	$242.5882	$242.59	$242.60	$242.60
Purchase #2	$206.83	10.650%	$228.8574	$228.86	$228.85	$228.90
Purchase #3	$44.27	12.620%	$49.8569	$49.86	$49.85	$49.90
Purchase #4	$209.87	9.820%	$230.4792	$230.48	$230.50	$230.50
Purchase #5	$226.86	5.119%	$238.473	$238.47	$238.45	$238.50
Purchase #6	$146.56	3.272%	$151.3554	$151.36	$151.35	$151.40
Purchase #7	$88.53	11.681%	$98.8712	$98.87	$98.85	$98.90
7 purchase totals =	$1,154.78		$1,240.4813	$1,240.49	$1,240.45	$1,240.70