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	$74.28	6.185%	$78.8742	$78.87	$78.85	$78.90
Purchase #2	$137.35	9.817%	$150.8336	$150.83	$150.85	$150.80
Purchase #3	$215.29	6.546%	$229.3829	$229.38	$229.40	$229.40
Purchase #4	$204.71	4.374%	$213.664	$213.66	$213.65	$213.70
Purchase #5	$30.68	7.177%	$32.8819	$32.88	$32.90	$32.90
Purchase #6	$152.30	4.343%	$158.9144	$158.91	$158.90	$158.90
Purchase #7	$5.45	8.598%	$5.9186	$5.92	$5.90	$5.90
7 purchase totals =	$820.06		$870.4696	$870.45	$870.45	$870.50