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	$109.29	13.429%	$123.9666	$123.97	$123.95	$124.00
Purchase #2	$146.34	5.821%	$154.8585	$154.86	$154.85	$154.90
Purchase #3	$69.51	3.367%	$71.8504	$71.85	$71.85	$71.90
Purchase #4	$29.48	13.666%	$33.5087	$33.51	$33.50	$33.50
Purchase #5	$34.31	7.378%	$36.8414	$36.84	$36.85	$36.80
Purchase #6	$228.90	8.814%	$249.0752	$249.08	$249.10	$249.10
Purchase #7	$30.42	9.433%	$33.2895	$33.29	$33.30	$33.30
7 purchase totals =	$648.25		$703.3903	$703.40	$703.40	$703.50