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	$166.83	9.756%	$183.1059	$183.11	$183.10	$183.10
Purchase #2	$50.37	7.245%	$54.0193	$54.02	$54.00	$54.00
Purchase #3	$229.54	9.728%	$251.8697	$251.87	$251.85	$251.90
Purchase #4	$72.89	8.627%	$79.1782	$79.18	$79.20	$79.20
Purchase #5	$66.41	8.744%	$72.2169	$72.22	$72.20	$72.20
Purchase #6	$243.78	12.599%	$274.4938	$274.49	$274.50	$274.50
Purchase #7	$78.66	8.643%	$85.4586	$85.46	$85.45	$85.50
7 purchase totals =	$908.48		$1,000.3424	$1,000.35	$1,000.30	$1,000.40