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	$165.36	6.162%	$175.5495	$175.55	$175.55	$175.50
Purchase #2	$130.33	5.672%	$137.7223	$137.72	$137.70	$137.70
Purchase #3	$69.73	12.795%	$78.652	$78.65	$78.65	$78.70
Purchase #4	$33.25	3.497%	$34.4128	$34.41	$34.40	$34.40
Purchase #5	$23.71	11.624%	$26.4661	$26.47	$26.45	$26.50
Purchase #6	$13.32	6.410%	$14.1738	$14.17	$14.15	$14.20
Purchase #7	$59.30	3.660%	$61.4704	$61.47	$61.45	$61.50
7 purchase totals =	$495.00		$528.4469	$528.44	$528.35	$528.50