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	$38.92	3.124%	$40.1359	$40.14	$40.15	$40.10
Purchase #2	$82.88	9.263%	$90.5572	$90.56	$90.55	$90.60
Purchase #3	$26.30	11.791%	$29.401	$29.40	$29.40	$29.40
Purchase #4	$70.64	4.798%	$74.0293	$74.03	$74.05	$74.00
Purchase #5	$230.36	4.359%	$240.4014	$240.40	$240.40	$240.40
Purchase #6	$243.45	7.321%	$261.273	$261.27	$261.25	$261.30
Purchase #7	$178.75	7.117%	$191.4716	$191.47	$191.45	$191.50
7 purchase totals =	$871.30		$927.2694	$927.27	$927.25	$927.30