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	$22.86	6.851%	$24.4261	$24.43	$24.45	$24.40
Purchase #2	$90.76	9.209%	$99.1181	$99.12	$99.10	$99.10
Purchase #3	$11.51	7.636%	$12.3889	$12.39	$12.40	$12.40
Purchase #4	$39.54	10.363%	$43.6375	$43.64	$43.65	$43.60
Purchase #5	$194.95	11.280%	$216.9404	$216.94	$216.95	$216.90
Purchase #6	$36.68	11.406%	$40.8637	$40.86	$40.85	$40.90
Purchase #7	$64.26	6.414%	$68.3816	$68.38	$68.40	$68.40
7 purchase totals =	$460.56		$505.7563	$505.76	$505.80	$505.70