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	$242.32	3.774%	$251.4652	$251.47	$251.45	$251.50
Purchase #2	$82.91	7.237%	$88.9102	$88.91	$88.90	$88.90
Purchase #3	$209.64	13.600%	$238.151	$238.15	$238.15	$238.20
Purchase #4	$38.59	11.859%	$43.1664	$43.17	$43.15	$43.20
Purchase #5	$186.27	5.169%	$195.8983	$195.90	$195.90	$195.90
Purchase #6	$64.45	3.687%	$66.8263	$66.83	$66.85	$66.80
Purchase #7	$81.59	10.739%	$90.352	$90.35	$90.35	$90.40
7 purchase totals =	$905.77		$974.7694	$974.78	$974.75	$974.90