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	$72.41	6.220%	$76.9139	$76.91	$76.90	$76.90
Purchase #2	$63.93	9.490%	$69.997	$70.00	$70.00	$70.00
Purchase #3	$69.45	13.508%	$78.8313	$78.83	$78.85	$78.80
Purchase #4	$49.90	5.456%	$52.6225	$52.62	$52.60	$52.60
Purchase #5	$185.29	4.482%	$193.5947	$193.59	$193.60	$193.60
Purchase #6	$15.81	13.854%	$18.0003	$18.00	$18.00	$18.00
Purchase #7	$183.99	3.790%	$190.9632	$190.96	$190.95	$191.00
7 purchase totals =	$640.78		$680.9229	$680.91	$680.90	$680.90