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	$70.41	11.791%	$78.712	$78.71	$78.70	$78.70
Purchase #2	$220.56	13.600%	$250.5562	$250.56	$250.55	$250.60
Purchase #3	$139.88	12.477%	$157.3328	$157.33	$157.35	$157.30
Purchase #4	$195.87	10.381%	$216.2033	$216.20	$216.20	$216.20
Purchase #5	$75.48	10.355%	$83.296	$83.30	$83.30	$83.30
Purchase #6	$51.27	5.574%	$54.1278	$54.13	$54.15	$54.10
Purchase #7	$21.53	4.397%	$22.4767	$22.48	$22.50	$22.50
7 purchase totals =	$775.00		$862.7048	$862.71	$862.75	$862.70