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	$178.66	11.698%	$199.5596	$199.56	$199.55	$199.60
Purchase #2	$178.32	13.313%	$202.0597	$202.06	$202.05	$202.10
Purchase #3	$78.91	5.368%	$83.1459	$83.15	$83.15	$83.10
Purchase #4	$71.72	8.860%	$78.0744	$78.07	$78.05	$78.10
Purchase #5	$40.86	3.855%	$42.4352	$42.44	$42.45	$42.40
Purchase #6	$44.87	7.507%	$48.2384	$48.24	$48.25	$48.20
Purchase #7	$210.94	11.850%	$235.9364	$235.94	$235.95	$235.90
7 purchase totals =	$804.28		$889.4496	$889.46	$889.45	$889.40