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	$42.72	6.223%	$45.3785	$45.38	$45.40	$45.40
Purchase #2	$172.25	9.743%	$189.0323	$189.03	$189.05	$189.00
Purchase #3	$233.79	11.743%	$261.244	$261.24	$261.25	$261.20
Purchase #4	$45.98	13.221%	$52.059	$52.06	$52.05	$52.10
Purchase #5	$120.59	13.744%	$137.1639	$137.16	$137.15	$137.20
Purchase #6	$16.96	7.744%	$18.2734	$18.27	$18.25	$18.30
Purchase #7	$223.91	10.511%	$247.4452	$247.45	$247.45	$247.40
7 purchase totals =	$856.20		$950.5963	$950.59	$950.60	$950.60