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	$123.72	10.195%	$136.3333	$136.33	$136.35	$136.30
Purchase #2	$54.68	12.820%	$61.69	$61.69	$61.70	$61.70
Purchase #3	$202.54	11.535%	$225.903	$225.90	$225.90	$225.90
Purchase #4	$186.84	12.247%	$209.7223	$209.72	$209.70	$209.70
Purchase #5	$224.55	10.471%	$248.0626	$248.06	$248.05	$248.10
Purchase #6	$30.43	13.725%	$34.6065	$34.61	$34.60	$34.60
Purchase #7	$59.35	13.156%	$67.1581	$67.16	$67.15	$67.20
7 purchase totals =	$882.11		$983.4758	$983.47	$983.45	$983.50