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	$234.55	10.615%	$259.4475	$259.45	$259.45	$259.40
Purchase #2	$160.26	13.465%	$181.839	$181.84	$181.85	$181.80
Purchase #3	$45.86	7.538%	$49.3169	$49.32	$49.30	$49.30
Purchase #4	$38.38	10.183%	$42.2882	$42.29	$42.30	$42.30
Purchase #5	$206.25	3.361%	$213.1821	$213.18	$213.20	$213.20
Purchase #6	$79.27	13.689%	$90.1213	$90.12	$90.10	$90.10
Purchase #7	$89.55	3.550%	$92.729	$92.73	$92.75	$92.70
7 purchase totals =	$854.12		$928.9240	$928.93	$928.95	$928.80