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	$104.47	10.770%	$115.7214	$115.72	$115.70	$115.70
Purchase #2	$76.29	7.672%	$82.143	$82.14	$82.15	$82.10
Purchase #3	$232.32	10.750%	$257.2944	$257.29	$257.30	$257.30
Purchase #4	$61.86	7.190%	$66.3077	$66.31	$66.30	$66.30
Purchase #5	$59.94	4.675%	$62.7422	$62.74	$62.75	$62.70
Purchase #6	$48.87	10.122%	$53.8166	$53.82	$53.80	$53.80
Purchase #7	$169.58	7.803%	$182.8123	$182.81	$182.80	$182.80
7 purchase totals =	$753.33		$820.8376	$820.83	$820.80	$820.70