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	$38.51	11.352%	$42.8817	$42.88	$42.90	$42.90
Purchase #2	$94.54	4.809%	$99.0864	$99.09	$99.10	$99.10
Purchase #3	$157.65	13.438%	$178.835	$178.84	$178.85	$178.80
Purchase #4	$96.25	3.795%	$99.9027	$99.90	$99.90	$99.90
Purchase #5	$240.81	11.724%	$269.0426	$269.04	$269.05	$269.00
Purchase #6	$229.88	11.104%	$255.4059	$255.41	$255.40	$255.40
Purchase #7	$103.27	5.158%	$108.5967	$108.60	$108.60	$108.60
7 purchase totals =	$960.91		$1,053.7510	$1,053.76	$1,053.80	$1,053.70