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	$55.72	6.272%	$59.2148	$59.21	$59.20	$59.20
Purchase #2	$223.59	4.697%	$234.092	$234.09	$234.10	$234.10
Purchase #3	$227.67	13.359%	$258.0844	$258.08	$258.10	$258.10
Purchase #4	$153.75	5.132%	$161.6405	$161.64	$161.65	$161.60
Purchase #5	$65.68	7.206%	$70.4129	$70.41	$70.40	$70.40
Purchase #6	$40.42	5.221%	$42.5303	$42.53	$42.55	$42.50
Purchase #7	$20.27	3.124%	$20.9032	$20.90	$20.90	$20.90
7 purchase totals =	$787.10		$846.8781	$846.86	$846.90	$846.80