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	$234.74	3.728%	$243.4911	$243.49	$243.50	$243.50
Purchase #2	$35.77	12.126%	$40.1075	$40.11	$40.10	$40.10
Purchase #3	$167.48	12.839%	$188.9828	$188.98	$189.00	$189.00
Purchase #4	$45.36	9.113%	$49.4937	$49.49	$49.50	$49.50
Purchase #5	$56.31	12.710%	$63.467	$63.47	$63.45	$63.50
Purchase #6	$27.33	4.664%	$28.6047	$28.60	$28.60	$28.60
Purchase #7	$48.28	6.144%	$51.2463	$51.25	$51.25	$51.20
7 purchase totals =	$615.27		$665.3931	$665.39	$665.40	$665.40