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	$45.58	3.267%	$47.0691	$47.07	$47.05	$47.10
Purchase #2	$53.78	3.125%	$55.4606	$55.46	$55.45	$55.50
Purchase #3	$42.26	3.672%	$43.8118	$43.81	$43.80	$43.80
Purchase #4	$43.40	11.254%	$48.2842	$48.28	$48.30	$48.30
Purchase #5	$159.88	11.632%	$178.4772	$178.48	$178.50	$178.50
Purchase #6	$49.61	7.798%	$53.4786	$53.48	$53.50	$53.50
Purchase #7	$211.79	12.570%	$238.412	$238.41	$238.40	$238.40
7 purchase totals =	$606.30		$664.9935	$664.99	$665.00	$665.10