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	$50.71	7.507%	$54.5168	$54.52	$54.50	$54.50
Purchase #2	$6.67	9.240%	$7.2863	$7.29	$7.30	$7.30
Purchase #3	$46.40	11.697%	$51.8274	$51.83	$51.85	$51.80
Purchase #4	$169.26	4.167%	$176.3131	$176.31	$176.30	$176.30
Purchase #5	$111.46	3.662%	$115.5417	$115.54	$115.55	$115.50
Purchase #6	$20.74	10.695%	$22.9581	$22.96	$22.95	$23.00
Purchase #7	$156.53	5.311%	$164.8433	$164.84	$164.85	$164.80
7 purchase totals =	$561.77		$593.2867	$593.29	$593.30	$593.20