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	$136.46	5.627%	$144.1386	$144.14	$144.15	$144.10
Purchase #2	$48.71	10.297%	$53.7257	$53.73	$53.75	$53.70
Purchase #3	$220.79	13.585%	$250.7843	$250.78	$250.80	$250.80
Purchase #4	$144.75	8.303%	$156.7686	$156.77	$156.75	$156.80
Purchase #5	$97.53	3.446%	$100.8909	$100.89	$100.90	$100.90
Purchase #6	$7.40	10.182%	$8.1535	$8.15	$8.15	$8.20
Purchase #7	$23.34	3.498%	$24.1564	$24.16	$24.15	$24.20
7 purchase totals =	$678.98		$738.6180	$738.62	$738.65	$738.70