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	$49.95	6.236%	$53.0649	$53.06	$53.05	$53.10
Purchase #2	$186.77	12.527%	$210.1667	$210.17	$210.15	$210.20
Purchase #3	$74.65	9.588%	$81.8074	$81.81	$81.80	$81.80
Purchase #4	$159.55	4.556%	$166.8191	$166.82	$166.80	$166.80
Purchase #5	$146.69	12.124%	$164.4747	$164.47	$164.45	$164.50
Purchase #6	$31.31	6.684%	$33.4028	$33.40	$33.40	$33.40
Purchase #7	$156.93	9.844%	$172.3782	$172.38	$172.40	$172.40
7 purchase totals =	$805.85		$882.1138	$882.11	$882.05	$882.20