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	$120.85	5.559%	$127.5681	$127.57	$127.55	$127.60
Purchase #2	$221.86	10.184%	$244.4542	$244.45	$244.45	$244.50
Purchase #3	$64.72	12.756%	$72.9757	$72.98	$73.00	$73.00
Purchase #4	$240.46	8.829%	$261.6902	$261.69	$261.70	$261.70
Purchase #5	$96.71	3.638%	$100.2283	$100.23	$100.25	$100.20
Purchase #6	$74.63	5.617%	$78.822	$78.82	$78.80	$78.80
Purchase #7	$36.54	10.517%	$40.3829	$40.38	$40.40	$40.40
7 purchase totals =	$855.77		$926.1214	$926.12	$926.15	$926.20