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	$19.49	10.769%	$21.5889	$21.59	$21.60	$21.60
Purchase #2	$186.78	10.468%	$206.3321	$206.33	$206.35	$206.30
Purchase #3	$203.38	4.626%	$212.7884	$212.79	$212.80	$212.80
Purchase #4	$158.63	5.412%	$167.2151	$167.22	$167.20	$167.20
Purchase #5	$134.33	13.768%	$152.8246	$152.82	$152.80	$152.80
Purchase #6	$110.91	8.256%	$120.0667	$120.07	$120.05	$120.10
Purchase #7	$207.55	11.328%	$231.0613	$231.06	$231.05	$231.10
7 purchase totals =	$1,021.07		$1,111.8771	$1,111.88	$1,111.85	$1,111.90