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	$231.64	10.204%	$255.2765	$255.28	$255.30	$255.30
Purchase #2	$177.88	4.130%	$185.2264	$185.23	$185.25	$185.20
Purchase #3	$82.82	3.623%	$85.8206	$85.82	$85.80	$85.80
Purchase #4	$132.43	6.156%	$140.5824	$140.58	$140.60	$140.60
Purchase #5	$243.89	9.744%	$267.6546	$267.65	$267.65	$267.70
Purchase #6	$58.37	13.685%	$66.3579	$66.36	$66.35	$66.40
Purchase #7	$100.92	9.646%	$110.6547	$110.65	$110.65	$110.70
7 purchase totals =	$1,027.95		$1,111.5731	$1,111.57	$1,111.60	$1,111.70