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	$57.39	4.403%	$59.9169	$59.92	$59.90	$59.90
Purchase #2	$223.68	6.552%	$238.3355	$238.34	$238.35	$238.30
Purchase #3	$136.83	3.819%	$142.0555	$142.06	$142.05	$142.10
Purchase #4	$146.41	6.244%	$155.5518	$155.55	$155.55	$155.60
Purchase #5	$133.85	9.687%	$146.816	$146.82	$146.80	$146.80
Purchase #6	$232.59	9.666%	$255.0721	$255.07	$255.05	$255.10
Purchase #7	$13.31	13.344%	$15.0861	$15.09	$15.10	$15.10
7 purchase totals =	$944.06		$1,012.8339	$1,012.85	$1,012.80	$1,012.90