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	$83.71	7.621%	$90.0895	$90.09	$90.10	$90.10
Purchase #2	$47.70	5.697%	$50.4175	$50.42	$50.40	$50.40
Purchase #3	$199.61	4.751%	$209.0935	$209.09	$209.10	$209.10
Purchase #4	$145.32	7.215%	$155.8048	$155.80	$155.80	$155.80
Purchase #5	$116.64	6.550%	$124.2799	$124.28	$124.30	$124.30
Purchase #6	$68.58	13.705%	$77.9789	$77.98	$78.00	$78.00
Purchase #7	$131.88	8.845%	$143.5448	$143.54	$143.55	$143.50
7 purchase totals =	$793.44		$851.2089	$851.20	$851.25	$851.20