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	$108.83	5.353%	$114.6557	$114.66	$114.65	$114.70
Purchase #2	$76.58	4.322%	$79.8898	$79.89	$79.90	$79.90
Purchase #3	$52.75	12.505%	$59.3464	$59.35	$59.35	$59.30
Purchase #4	$128.45	12.194%	$144.1132	$144.11	$144.10	$144.10
Purchase #5	$18.71	13.182%	$21.1764	$21.18	$21.20	$21.20
Purchase #6	$76.35	13.714%	$86.8206	$86.82	$86.80	$86.80
Purchase #7	$146.73	12.577%	$165.1842	$165.18	$165.20	$165.20
7 purchase totals =	$608.40		$671.1863	$671.19	$671.20	$671.20