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	$64.65	10.192%	$71.2391	$71.24	$71.25	$71.20
Purchase #2	$19.77	4.334%	$20.6268	$20.63	$20.65	$20.60
Purchase #3	$118.94	7.218%	$127.5251	$127.53	$127.55	$127.50
Purchase #4	$163.59	12.518%	$184.0682	$184.07	$184.05	$184.10
Purchase #5	$236.58	10.650%	$261.7758	$261.78	$261.80	$261.80
Purchase #6	$38.48	11.266%	$42.8152	$42.82	$42.80	$42.80
Purchase #7	$77.70	6.356%	$82.6386	$82.64	$82.65	$82.60
7 purchase totals =	$719.71		$790.6888	$790.71	$790.75	$790.60