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	$55.83	5.852%	$59.0972	$59.10	$59.10	$59.10
Purchase #2	$85.72	13.694%	$97.4585	$97.46	$97.45	$97.50
Purchase #3	$174.28	13.773%	$198.2836	$198.28	$198.30	$198.30
Purchase #4	$185.70	10.589%	$205.3638	$205.36	$205.35	$205.40
Purchase #5	$132.83	6.623%	$141.6273	$141.63	$141.65	$141.60
Purchase #6	$30.90	4.139%	$32.179	$32.18	$32.20	$32.20
Purchase #7	$39.77	5.708%	$42.0401	$42.04	$42.05	$42.00
7 purchase totals =	$705.03		$776.0495	$776.05	$776.10	$776.10