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	$68.78	12.837%	$77.6093	$77.61	$77.60	$77.60
Purchase #2	$128.34	8.405%	$139.127	$139.13	$139.15	$139.10
Purchase #3	$35.65	10.398%	$39.3569	$39.36	$39.35	$39.40
Purchase #4	$204.47	3.598%	$211.8268	$211.83	$211.85	$211.80
Purchase #5	$175.98	11.707%	$196.582	$196.58	$196.60	$196.60
Purchase #6	$231.61	11.700%	$258.7084	$258.71	$258.70	$258.70
Purchase #7	$71.26	8.222%	$77.119	$77.12	$77.10	$77.10
7 purchase totals =	$916.09		$1,000.3294	$1,000.34	$1,000.35	$1,000.30