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	$10.57	7.742%	$11.3883	$11.39	$11.40	$11.40
Purchase #2	$145.77	5.810%	$154.2392	$154.24	$154.25	$154.20
Purchase #3	$145.38	7.489%	$156.2675	$156.27	$156.25	$156.30
Purchase #4	$207.52	9.616%	$227.4751	$227.48	$227.50	$227.50
Purchase #5	$36.32	7.657%	$39.101	$39.10	$39.10	$39.10
Purchase #6	$48.54	3.556%	$50.2661	$50.27	$50.25	$50.30
Purchase #7	$26.31	10.309%	$29.0223	$29.02	$29.00	$29.00
7 purchase totals =	$620.41		$667.7595	$667.77	$667.75	$667.80