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	$76.45	3.218%	$78.9102	$78.91	$78.90	$78.90
Purchase #2	$40.72	5.371%	$42.9071	$42.91	$42.90	$42.90
Purchase #3	$142.45	3.423%	$147.3261	$147.33	$147.35	$147.30
Purchase #4	$243.32	10.596%	$269.1022	$269.10	$269.10	$269.10
Purchase #5	$149.83	6.216%	$159.1434	$159.14	$159.15	$159.10
Purchase #6	$8.25	13.671%	$9.3779	$9.38	$9.40	$9.40
Purchase #7	$166.29	7.555%	$178.8532	$178.85	$178.85	$178.90
7 purchase totals =	$827.31		$885.6201	$885.62	$885.65	$885.60