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	$115.54	6.838%	$123.4406	$123.44	$123.45	$123.40
Purchase #2	$64.47	10.760%	$71.407	$71.41	$71.40	$71.40
Purchase #3	$160.96	5.416%	$169.6776	$169.68	$169.70	$169.70
Purchase #4	$81.42	10.494%	$89.9642	$89.96	$89.95	$90.00
Purchase #5	$74.71	4.221%	$77.8635	$77.86	$77.85	$77.90
Purchase #6	$88.27	10.514%	$97.5507	$97.55	$97.55	$97.60
Purchase #7	$132.82	5.155%	$139.6669	$139.67	$139.65	$139.70
7 purchase totals =	$718.19		$769.5705	$769.57	$769.55	$769.70