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	$12.90	3.415%	$13.3405	$13.34	$13.35	$13.30
Purchase #2	$226.63	6.289%	$240.8828	$240.88	$240.90	$240.90
Purchase #3	$44.76	10.873%	$49.6268	$49.63	$49.65	$49.60
Purchase #4	$96.76	12.666%	$109.0156	$109.02	$109.00	$109.00
Purchase #5	$91.76	9.608%	$100.5763	$100.58	$100.60	$100.60
Purchase #6	$171.39	13.413%	$194.3785	$194.38	$194.40	$194.40
Purchase #7	$19.86	13.519%	$22.5449	$22.54	$22.55	$22.50
7 purchase totals =	$664.06		$730.3654	$730.37	$730.45	$730.30