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	$137.95	4.124%	$143.6391	$143.64	$143.65	$143.60
Purchase #2	$171.31	8.504%	$185.8782	$185.88	$185.90	$185.90
Purchase #3	$198.49	8.238%	$214.8416	$214.84	$214.85	$214.80
Purchase #4	$72.71	3.614%	$75.3377	$75.34	$75.35	$75.30
Purchase #5	$138.25	3.685%	$143.3445	$143.34	$143.35	$143.30
Purchase #6	$76.29	7.831%	$82.2643	$82.26	$82.25	$82.30
Purchase #7	$127.33	4.313%	$132.8217	$132.82	$132.80	$132.80
7 purchase totals =	$922.33		$978.1271	$978.12	$978.15	$978.00