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	$77.71	5.286%	$81.8178	$81.82	$81.80	$81.80
Purchase #2	$214.83	8.239%	$232.5298	$232.53	$232.55	$232.50
Purchase #3	$94.50	11.793%	$105.6444	$105.64	$105.65	$105.60
Purchase #4	$37.91	13.849%	$43.1602	$43.16	$43.15	$43.20
Purchase #5	$239.77	10.751%	$265.5477	$265.55	$265.55	$265.50
Purchase #6	$27.61	4.820%	$28.9408	$28.94	$28.95	$28.90
Purchase #7	$248.48	3.870%	$258.0962	$258.10	$258.10	$258.10
7 purchase totals =	$940.81		$1,015.7369	$1,015.74	$1,015.75	$1,015.60