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	$241.78	11.690%	$270.0441	$270.04	$270.05	$270.00
Purchase #2	$229.44	11.774%	$256.4543	$256.45	$256.45	$256.50
Purchase #3	$196.26	10.546%	$216.9576	$216.96	$216.95	$217.00
Purchase #4	$32.83	8.637%	$35.6655	$35.67	$35.65	$35.70
Purchase #5	$43.30	4.619%	$45.3	$45.30	$45.30	$45.30
Purchase #6	$211.28	13.640%	$240.0986	$240.10	$240.10	$240.10
Purchase #7	$200.96	12.406%	$225.8911	$225.89	$225.90	$225.90
7 purchase totals =	$1,155.85		$1,290.4112	$1,290.41	$1,290.40	$1,290.50