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	$134.76	5.594%	$142.2985	$142.30	$142.30	$142.30
Purchase #2	$204.32	5.524%	$215.6066	$215.61	$215.60	$215.60
Purchase #3	$13.71	11.522%	$15.2897	$15.29	$15.30	$15.30
Purchase #4	$191.97	9.291%	$209.8059	$209.81	$209.80	$209.80
Purchase #5	$58.86	3.569%	$60.9607	$60.96	$60.95	$61.00
Purchase #6	$71.81	11.384%	$79.9849	$79.98	$80.00	$80.00
Purchase #7	$83.84	7.142%	$89.8279	$89.83	$89.85	$89.80
7 purchase totals =	$759.27		$813.7742	$813.78	$813.80	$813.80