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	$200.56	12.378%	$225.3853	$225.39	$225.40	$225.40
Purchase #2	$75.98	8.208%	$82.2164	$82.22	$82.20	$82.20
Purchase #3	$91.77	5.479%	$96.7981	$96.80	$96.80	$96.80
Purchase #4	$85.78	5.844%	$90.793	$90.79	$90.80	$90.80
Purchase #5	$32.36	8.442%	$35.0918	$35.09	$35.10	$35.10
Purchase #6	$86.35	4.746%	$90.4482	$90.45	$90.45	$90.40
Purchase #7	$68.82	9.149%	$75.1163	$75.12	$75.10	$75.10
7 purchase totals =	$641.62		$695.8491	$695.86	$695.85	$695.80