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	$5.32	11.767%	$5.946	$5.95	$5.95	$5.90
Purchase #2	$81.26	11.514%	$90.6163	$90.62	$90.60	$90.60
Purchase #3	$42.27	5.352%	$44.5323	$44.53	$44.55	$44.50
Purchase #4	$172.48	7.503%	$185.4212	$185.42	$185.40	$185.40
Purchase #5	$49.36	6.495%	$52.5659	$52.57	$52.55	$52.60
Purchase #6	$233.26	6.151%	$247.6078	$247.61	$247.60	$247.60
Purchase #7	$237.27	5.583%	$250.5168	$250.52	$250.50	$250.50
7 purchase totals =	$821.22		$877.2063	$877.22	$877.15	$877.10