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	$98.28	10.796%	$108.8903	$108.89	$108.90	$108.90
Purchase #2	$64.33	11.316%	$71.6096	$71.61	$71.60	$71.60
Purchase #3	$244.46	6.834%	$261.1664	$261.17	$261.15	$261.20
Purchase #4	$51.28	4.164%	$53.4153	$53.42	$53.40	$53.40
Purchase #5	$141.58	12.709%	$159.5734	$159.57	$159.55	$159.60
Purchase #6	$98.68	8.253%	$106.8241	$106.82	$106.80	$106.80
Purchase #7	$221.61	10.713%	$245.3511	$245.35	$245.35	$245.40
7 purchase totals =	$920.22		$1,006.8302	$1,006.83	$1,006.75	$1,006.90