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	$129.56	11.803%	$144.852	$144.85	$144.85	$144.90
Purchase #2	$167.93	10.663%	$185.8364	$185.84	$185.85	$185.80
Purchase #3	$39.96	6.425%	$42.5274	$42.53	$42.55	$42.50
Purchase #4	$123.45	13.421%	$140.0182	$140.02	$140.00	$140.00
Purchase #5	$90.64	10.733%	$100.3684	$100.37	$100.35	$100.40
Purchase #6	$230.44	8.731%	$250.5597	$250.56	$250.55	$250.60
Purchase #7	$60.36	8.132%	$65.2685	$65.27	$65.25	$65.30
7 purchase totals =	$842.34		$929.4306	$929.44	$929.40	$929.50