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	$178.25	3.806%	$185.0342	$185.03	$185.05	$185.00
Purchase #2	$52.80	7.473%	$56.7457	$56.75	$56.75	$56.70
Purchase #3	$39.69	9.108%	$43.305	$43.31	$43.30	$43.30
Purchase #4	$52.70	11.478%	$58.7489	$58.75	$58.75	$58.70
Purchase #5	$55.25	8.238%	$59.8015	$59.80	$59.80	$59.80
Purchase #6	$34.39	10.655%	$38.0543	$38.05	$38.05	$38.10
Purchase #7	$38.55	10.796%	$42.7119	$42.71	$42.70	$42.70
7 purchase totals =	$451.63		$484.4015	$484.40	$484.40	$484.30