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	$147.42	13.834%	$167.8141	$167.81	$167.80	$167.80
Purchase #2	$96.38	13.111%	$109.0164	$109.02	$109.00	$109.00
Purchase #3	$13.84	9.135%	$15.1043	$15.10	$15.10	$15.10
Purchase #4	$194.70	12.146%	$218.3483	$218.35	$218.35	$218.30
Purchase #5	$83.56	6.608%	$89.0816	$89.08	$89.10	$89.10
Purchase #6	$12.67	9.577%	$13.8834	$13.88	$13.90	$13.90
Purchase #7	$117.27	13.331%	$132.9033	$132.90	$132.90	$132.90
7 purchase totals =	$665.84		$746.1514	$746.14	$746.15	$746.10