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	$135.41	6.263%	$143.8907	$143.89	$143.90	$143.90
Purchase #2	$24.86	8.842%	$27.0581	$27.06	$27.05	$27.10
Purchase #3	$243.75	8.548%	$264.5858	$264.59	$264.60	$264.60
Purchase #4	$127.52	10.123%	$140.4288	$140.43	$140.45	$140.40
Purchase #5	$197.30	7.421%	$211.9416	$211.94	$211.95	$211.90
Purchase #6	$81.88	6.226%	$86.9778	$86.98	$87.00	$87.00
Purchase #7	$105.83	5.652%	$111.8115	$111.81	$111.80	$111.80
7 purchase totals =	$916.55		$986.6943	$986.70	$986.75	$986.70