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	$35.34	4.454%	$36.914	$36.91	$36.90	$36.90
Purchase #2	$158.97	10.789%	$176.1213	$176.12	$176.10	$176.10
Purchase #3	$230.58	4.412%	$240.7532	$240.75	$240.75	$240.80
Purchase #4	$85.77	5.685%	$90.646	$90.65	$90.65	$90.60
Purchase #5	$71.87	13.470%	$81.5509	$81.55	$81.55	$81.60
Purchase #6	$125.48	12.682%	$141.3934	$141.39	$141.40	$141.40
Purchase #7	$102.51	10.758%	$113.538	$113.54	$113.55	$113.50
7 purchase totals =	$810.52		$880.9168	$880.91	$880.90	$880.90