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	$99.38	12.163%	$111.4676	$111.47	$111.45	$111.50
Purchase #2	$231.71	3.292%	$239.3379	$239.34	$239.35	$239.30
Purchase #3	$77.55	9.814%	$85.1608	$85.16	$85.15	$85.20
Purchase #4	$156.43	9.719%	$171.6334	$171.63	$171.65	$171.60
Purchase #5	$29.27	11.779%	$32.7177	$32.72	$32.70	$32.70
Purchase #6	$51.43	8.499%	$55.801	$55.80	$55.80	$55.80
Purchase #7	$40.43	7.291%	$43.3778	$43.38	$43.40	$43.40
7 purchase totals =	$686.20		$739.4962	$739.50	$739.50	$739.50