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	$136.53	5.720%	$144.3395	$144.34	$144.35	$144.30
Purchase #2	$186.98	7.347%	$200.7174	$200.72	$200.70	$200.70
Purchase #3	$39.66	4.321%	$41.3737	$41.37	$41.35	$41.40
Purchase #4	$229.92	5.390%	$242.3127	$242.31	$242.30	$242.30
Purchase #5	$139.73	6.542%	$148.8711	$148.87	$148.85	$148.90
Purchase #6	$226.73	5.336%	$238.8283	$238.83	$238.85	$238.80
Purchase #7	$90.96	8.411%	$98.6106	$98.61	$98.60	$98.60
7 purchase totals =	$1,050.51		$1,115.0533	$1,115.05	$1,115.00	$1,115.00