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	$238.87	4.449%	$249.4973	$249.50	$249.50	$249.50
Purchase #2	$105.48	5.344%	$111.1169	$111.12	$111.10	$111.10
Purchase #3	$39.34	8.799%	$42.8015	$42.80	$42.80	$42.80
Purchase #4	$120.56	9.476%	$131.9843	$131.98	$132.00	$132.00
Purchase #5	$173.26	8.619%	$188.1933	$188.19	$188.20	$188.20
Purchase #6	$85.68	5.400%	$90.3067	$90.31	$90.30	$90.30
Purchase #7	$250.66	6.424%	$266.7624	$266.76	$266.75	$266.80
7 purchase totals =	$1,013.85		$1,080.6624	$1,080.66	$1,080.65	$1,080.70