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	$149.32	12.777%	$168.3986	$168.40	$168.40	$168.40
Purchase #2	$175.61	5.538%	$185.3353	$185.34	$185.35	$185.30
Purchase #3	$96.92	10.164%	$106.7709	$106.77	$106.75	$106.80
Purchase #4	$153.34	4.172%	$159.7373	$159.74	$159.75	$159.70
Purchase #5	$66.62	7.150%	$71.3833	$71.38	$71.40	$71.40
Purchase #6	$75.99	13.486%	$86.238	$86.24	$86.25	$86.20
Purchase #7	$80.58	12.613%	$90.7436	$90.74	$90.75	$90.70
7 purchase totals =	$798.38		$868.6070	$868.61	$868.65	$868.50