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	$88.55	12.302%	$99.4434	$99.44	$99.45	$99.40
Purchase #2	$241.78	5.678%	$255.5083	$255.51	$255.50	$255.50
Purchase #3	$135.56	7.635%	$145.91	$145.91	$145.90	$145.90
Purchase #4	$134.31	10.728%	$148.7188	$148.72	$148.70	$148.70
Purchase #5	$69.37	3.106%	$71.5246	$71.52	$71.50	$71.50
Purchase #6	$230.85	4.161%	$240.4557	$240.46	$240.45	$240.50
Purchase #7	$24.25	7.425%	$26.0506	$26.05	$26.05	$26.10
7 purchase totals =	$924.67		$987.6114	$987.61	$987.55	$987.60