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	$42.30	13.277%	$47.9162	$47.92	$47.90	$47.90
Purchase #2	$52.61	3.420%	$54.4093	$54.41	$54.40	$54.40
Purchase #3	$56.51	5.555%	$59.6491	$59.65	$59.65	$59.60
Purchase #4	$122.47	7.412%	$131.5475	$131.55	$131.55	$131.50
Purchase #5	$96.74	8.756%	$105.2106	$105.21	$105.20	$105.20
Purchase #6	$235.38	4.856%	$246.8101	$246.81	$246.80	$246.80
Purchase #7	$126.43	7.147%	$135.466	$135.47	$135.45	$135.50
7 purchase totals =	$732.44		$781.0088	$781.02	$780.95	$780.90