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	$14.38	6.170%	$15.2672	$15.27	$15.25	$15.30
Purchase #2	$213.55	12.562%	$240.3762	$240.38	$240.40	$240.40
Purchase #3	$184.57	3.819%	$191.6187	$191.62	$191.60	$191.60
Purchase #4	$182.47	3.644%	$189.1192	$189.12	$189.10	$189.10
Purchase #5	$46.89	4.282%	$48.8978	$48.90	$48.90	$48.90
Purchase #6	$104.54	6.390%	$111.2201	$111.22	$111.20	$111.20
Purchase #7	$90.68	13.332%	$102.7695	$102.77	$102.75	$102.80
7 purchase totals =	$837.08		$899.2687	$899.28	$899.20	$899.30