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	$68.32	6.678%	$72.8824	$72.88	$72.90	$72.90
Purchase #2	$234.43	6.725%	$250.1954	$250.20	$250.20	$250.20
Purchase #3	$155.32	10.276%	$171.2807	$171.28	$171.30	$171.30
Purchase #4	$247.64	10.874%	$274.5684	$274.57	$274.55	$274.60
Purchase #5	$88.66	12.761%	$99.9739	$99.97	$99.95	$100.00
Purchase #6	$122.32	4.665%	$128.0262	$128.03	$128.05	$128.00
Purchase #7	$25.51	12.464%	$28.6896	$28.69	$28.70	$28.70
7 purchase totals =	$942.20		$1,025.6166	$1,025.62	$1,025.65	$1,025.70