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	$139.47	11.333%	$155.2761	$155.28	$155.30	$155.30
Purchase #2	$105.37	4.261%	$109.8598	$109.86	$109.85	$109.90
Purchase #3	$103.85	5.519%	$109.5815	$109.58	$109.60	$109.60
Purchase #4	$175.39	3.498%	$181.5251	$181.53	$181.55	$181.50
Purchase #5	$9.94	8.454%	$10.7803	$10.78	$10.80	$10.80
Purchase #6	$186.75	12.706%	$210.4785	$210.48	$210.50	$210.50
Purchase #7	$140.30	8.737%	$152.558	$152.56	$152.55	$152.60
7 purchase totals =	$861.07		$930.0593	$930.07	$930.15	$930.20