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	$123.46	11.157%	$137.2344	$137.23	$137.25	$137.20
Purchase #2	$112.62	9.584%	$123.4135	$123.41	$123.40	$123.40
Purchase #3	$36.72	11.199%	$40.8323	$40.83	$40.85	$40.80
Purchase #4	$224.67	10.283%	$247.7728	$247.77	$247.75	$247.80
Purchase #5	$38.75	12.306%	$43.5186	$43.52	$43.50	$43.50
Purchase #6	$49.73	7.815%	$53.6164	$53.62	$53.60	$53.60
Purchase #7	$6.75	6.115%	$7.1628	$7.16	$7.15	$7.20
7 purchase totals =	$592.70		$653.5508	$653.54	$653.50	$653.50