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	$74.47	10.519%	$82.3035	$82.30	$82.30	$82.30
Purchase #2	$222.43	10.521%	$245.8319	$245.83	$245.85	$245.80
Purchase #3	$175.88	5.139%	$184.9185	$184.92	$184.90	$184.90
Purchase #4	$27.93	8.683%	$30.3552	$30.36	$30.35	$30.40
Purchase #5	$42.85	12.630%	$48.262	$48.26	$48.25	$48.30
Purchase #6	$59.65	10.293%	$65.7898	$65.79	$65.80	$65.80
Purchase #7	$82.94	7.420%	$89.0941	$89.09	$89.10	$89.10
7 purchase totals =	$686.15		$746.5550	$746.55	$746.55	$746.60