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	$120.62	6.221%	$128.1238	$128.12	$128.10	$128.10
Purchase #2	$91.94	12.196%	$103.153	$103.15	$103.15	$103.20
Purchase #3	$111.77	11.447%	$124.5643	$124.56	$124.55	$124.60
Purchase #4	$241.88	3.696%	$250.8199	$250.82	$250.80	$250.80
Purchase #5	$154.58	9.298%	$168.9528	$168.95	$168.95	$169.00
Purchase #6	$20.63	3.707%	$21.3948	$21.39	$21.40	$21.40
Purchase #7	$114.99	3.395%	$118.8939	$118.89	$118.90	$118.90
7 purchase totals =	$856.41		$915.9025	$915.88	$915.85	$916.00