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	$202.25	12.758%	$228.0531	$228.05	$228.05	$228.10
Purchase #2	$54.62	12.612%	$61.5087	$61.51	$61.50	$61.50
Purchase #3	$47.78	9.781%	$52.4534	$52.45	$52.45	$52.50
Purchase #4	$56.43	13.230%	$63.8957	$63.90	$63.90	$63.90
Purchase #5	$53.54	11.320%	$59.6007	$59.60	$59.60	$59.60
Purchase #6	$208.86	6.641%	$222.7304	$222.73	$222.75	$222.70
Purchase #7	$172.50	3.664%	$178.8204	$178.82	$178.80	$178.80
7 purchase totals =	$795.98		$867.0624	$867.06	$867.05	$867.10