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	$53.35	9.583%	$58.4625	$58.46	$58.45	$58.50
Purchase #2	$179.57	10.581%	$198.5703	$198.57	$198.55	$198.60
Purchase #3	$49.65	6.807%	$53.0297	$53.03	$53.05	$53.00
Purchase #4	$67.95	3.850%	$70.5661	$70.57	$70.55	$70.60
Purchase #5	$150.88	4.308%	$157.3799	$157.38	$157.40	$157.40
Purchase #6	$153.74	12.765%	$173.3649	$173.36	$173.35	$173.40
Purchase #7	$122.90	12.209%	$137.9049	$137.90	$137.90	$137.90
7 purchase totals =	$778.04		$849.2783	$849.27	$849.25	$849.40