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	$97.69	5.682%	$103.2407	$103.24	$103.25	$103.20
Purchase #2	$179.41	9.469%	$196.3983	$196.40	$196.40	$196.40
Purchase #3	$204.38	11.760%	$228.4151	$228.42	$228.40	$228.40
Purchase #4	$119.28	7.649%	$128.4037	$128.40	$128.40	$128.40
Purchase #5	$48.85	3.830%	$50.721	$50.72	$50.70	$50.70
Purchase #6	$63.89	7.479%	$68.6683	$68.67	$68.65	$68.70
Purchase #7	$202.95	3.697%	$210.4531	$210.45	$210.45	$210.50
7 purchase totals =	$916.45		$986.3002	$986.30	$986.25	$986.30