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	$245.70	8.861%	$267.4715	$267.47	$267.45	$267.50
Purchase #2	$127.84	10.732%	$141.5598	$141.56	$141.55	$141.60
Purchase #3	$178.32	6.430%	$189.786	$189.79	$189.80	$189.80
Purchase #4	$13.53	11.764%	$15.1217	$15.12	$15.10	$15.10
Purchase #5	$59.94	12.751%	$67.5829	$67.58	$67.60	$67.60
Purchase #6	$123.37	4.208%	$128.5614	$128.56	$128.55	$128.60
Purchase #7	$92.34	13.834%	$105.1143	$105.11	$105.10	$105.10
7 purchase totals =	$841.04		$915.1976	$915.19	$915.15	$915.30