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	$50.83	9.832%	$55.8276	$55.83	$55.85	$55.80
Purchase #2	$63.98	11.125%	$71.0978	$71.10	$71.10	$71.10
Purchase #3	$117.85	10.663%	$130.4163	$130.42	$130.40	$130.40
Purchase #4	$39.67	12.872%	$44.7763	$44.78	$44.80	$44.80
Purchase #5	$100.27	12.144%	$112.4468	$112.45	$112.45	$112.40
Purchase #6	$31.35	13.289%	$35.5161	$35.52	$35.50	$35.50
Purchase #7	$214.47	4.465%	$224.0461	$224.05	$224.05	$224.00
7 purchase totals =	$618.42		$674.1270	$674.15	$674.15	$674.00