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	$70.98	11.817%	$79.3677	$79.37	$79.35	$79.40
Purchase #2	$190.69	12.212%	$213.9771	$213.98	$214.00	$214.00
Purchase #3	$159.44	8.755%	$173.399	$173.40	$173.40	$173.40
Purchase #4	$98.47	6.483%	$104.8538	$104.85	$104.85	$104.90
Purchase #5	$123.63	12.773%	$139.4213	$139.42	$139.40	$139.40
Purchase #6	$37.51	4.242%	$39.1012	$39.10	$39.10	$39.10
Purchase #7	$178.55	12.442%	$200.7652	$200.77	$200.75	$200.80
7 purchase totals =	$859.27		$950.8853	$950.89	$950.85	$951.00