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	$99.25	10.681%	$109.8509	$109.85	$109.85	$109.90
Purchase #2	$83.26	6.740%	$88.8717	$88.87	$88.85	$88.90
Purchase #3	$53.38	5.495%	$56.3132	$56.31	$56.30	$56.30
Purchase #4	$160.63	13.598%	$182.4725	$182.47	$182.45	$182.50
Purchase #5	$29.33	11.801%	$32.7912	$32.79	$32.80	$32.80
Purchase #6	$154.68	5.241%	$162.7868	$162.79	$162.80	$162.80
Purchase #7	$9.52	11.302%	$10.596	$10.60	$10.60	$10.60
7 purchase totals =	$590.05		$643.6823	$643.68	$643.65	$643.80