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	$41.28	10.181%	$45.4827	$45.48	$45.50	$45.50
Purchase #2	$87.44	13.712%	$99.4298	$99.43	$99.45	$99.40
Purchase #3	$101.89	5.219%	$107.2076	$107.21	$107.20	$107.20
Purchase #4	$27.76	4.717%	$29.0694	$29.07	$29.05	$29.10
Purchase #5	$11.89	3.407%	$12.2951	$12.30	$12.30	$12.30
Purchase #6	$189.82	4.666%	$198.677	$198.68	$198.70	$198.70
Purchase #7	$42.89	8.651%	$46.6004	$46.60	$46.60	$46.60
7 purchase totals =	$502.97		$538.7620	$538.77	$538.80	$538.80