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	$64.82	7.190%	$69.4806	$69.48	$69.50	$69.50
Purchase #2	$90.39	12.306%	$101.5134	$101.51	$101.50	$101.50
Purchase #3	$37.91	6.568%	$40.3999	$40.40	$40.40	$40.40
Purchase #4	$78.91	4.451%	$82.4223	$82.42	$82.40	$82.40
Purchase #5	$96.95	9.238%	$105.9062	$105.91	$105.90	$105.90
Purchase #6	$238.90	4.728%	$250.1952	$250.20	$250.20	$250.20
Purchase #7	$197.94	8.119%	$214.0107	$214.01	$214.00	$214.00
7 purchase totals =	$805.82		$863.9283	$863.93	$863.90	$863.90