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	$118.72	6.320%	$126.2231	$126.22	$126.20	$126.20
Purchase #2	$54.49	9.540%	$59.6883	$59.69	$59.70	$59.70
Purchase #3	$80.91	3.260%	$83.5477	$83.55	$83.55	$83.50
Purchase #4	$125.91	5.283%	$132.5618	$132.56	$132.55	$132.60
Purchase #5	$247.46	13.507%	$280.8844	$280.88	$280.90	$280.90
Purchase #6	$166.93	13.823%	$190.0047	$190.00	$190.00	$190.00
Purchase #7	$72.88	7.102%	$78.0559	$78.06	$78.05	$78.10
7 purchase totals =	$867.30		$950.9659	$950.96	$950.95	$951.00