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	$135.37	4.305%	$141.1977	$141.20	$141.20	$141.20
Purchase #2	$60.67	6.809%	$64.801	$64.80	$64.80	$64.80
Purchase #3	$162.79	11.475%	$181.4702	$181.47	$181.45	$181.50
Purchase #4	$206.32	8.735%	$224.3421	$224.34	$224.35	$224.30
Purchase #5	$207.43	3.806%	$215.3248	$215.32	$215.30	$215.30
Purchase #6	$82.49	9.808%	$90.5806	$90.58	$90.60	$90.60
Purchase #7	$53.43	13.284%	$60.5276	$60.53	$60.55	$60.50
7 purchase totals =	$908.50		$978.2440	$978.24	$978.25	$978.20