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	$85.91	5.661%	$90.7734	$90.77	$90.75	$90.80
Purchase #2	$156.98	8.570%	$170.4332	$170.43	$170.45	$170.40
Purchase #3	$111.88	13.608%	$127.1046	$127.10	$127.10	$127.10
Purchase #4	$110.29	10.684%	$122.0734	$122.07	$122.05	$122.10
Purchase #5	$212.30	4.592%	$222.0488	$222.05	$222.05	$222.00
Purchase #6	$34.73	8.374%	$37.6383	$37.64	$37.65	$37.60
Purchase #7	$169.35	10.383%	$186.9336	$186.93	$186.95	$186.90
7 purchase totals =	$881.44		$957.0053	$956.99	$957.00	$956.90