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	$222.79	6.578%	$237.4451	$237.45	$237.45	$237.40
Purchase #2	$214.84	10.817%	$238.0792	$238.08	$238.10	$238.10
Purchase #3	$48.79	8.752%	$53.0601	$53.06	$53.05	$53.10
Purchase #4	$40.30	11.427%	$44.9051	$44.91	$44.90	$44.90
Purchase #5	$11.85	3.142%	$12.2223	$12.22	$12.20	$12.20
Purchase #6	$28.61	9.696%	$31.384	$31.38	$31.40	$31.40
Purchase #7	$199.60	11.539%	$222.6318	$222.63	$222.65	$222.60
7 purchase totals =	$766.78		$839.7276	$839.73	$839.75	$839.70