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	$80.62	9.483%	$88.2652	$88.27	$88.25	$88.30
Purchase #2	$138.34	12.134%	$155.1262	$155.13	$155.15	$155.10
Purchase #3	$80.83	3.656%	$83.7851	$83.79	$83.80	$83.80
Purchase #4	$96.87	3.697%	$100.4513	$100.45	$100.45	$100.50
Purchase #5	$182.79	7.290%	$196.1154	$196.12	$196.10	$196.10
Purchase #6	$67.33	12.517%	$75.7577	$75.76	$75.75	$75.80
Purchase #7	$149.39	7.395%	$160.4374	$160.44	$160.45	$160.40
7 purchase totals =	$796.17		$859.9383	$859.96	$859.95	$860.00