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	$26.51	3.262%	$27.3748	$27.37	$27.35	$27.40
Purchase #2	$98.34	5.426%	$103.6759	$103.68	$103.70	$103.70
Purchase #3	$156.98	7.621%	$168.9434	$168.94	$168.95	$168.90
Purchase #4	$48.51	3.761%	$50.3345	$50.33	$50.35	$50.30
Purchase #5	$46.56	8.518%	$50.526	$50.53	$50.55	$50.50
Purchase #6	$204.37	8.857%	$222.4711	$222.47	$222.45	$222.50
Purchase #7	$105.42	5.686%	$111.4142	$111.41	$111.40	$111.40
7 purchase totals =	$686.69		$734.7399	$734.73	$734.75	$734.70