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	$26.80	3.468%	$27.7294	$27.73	$27.75	$27.70
Purchase #2	$71.60	9.800%	$78.6168	$78.62	$78.60	$78.60
Purchase #3	$6.93	3.624%	$7.1811	$7.18	$7.20	$7.20
Purchase #4	$155.32	6.204%	$164.9561	$164.96	$164.95	$165.00
Purchase #5	$136.76	8.438%	$148.2998	$148.30	$148.30	$148.30
Purchase #6	$64.47	12.369%	$72.4443	$72.44	$72.45	$72.40
Purchase #7	$247.62	13.340%	$280.6525	$280.65	$280.65	$280.70
7 purchase totals =	$709.50		$779.8800	$779.88	$779.90	$779.90