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	$127.91	6.388%	$136.0809	$136.08	$136.10	$136.10
Purchase #2	$170.73	13.820%	$194.3249	$194.32	$194.30	$194.30
Purchase #3	$67.67	9.228%	$73.9146	$73.91	$73.90	$73.90
Purchase #4	$231.30	3.816%	$240.1264	$240.13	$240.15	$240.10
Purchase #5	$145.45	3.723%	$150.8651	$150.87	$150.85	$150.90
Purchase #6	$159.52	13.694%	$181.3647	$181.36	$181.35	$181.40
Purchase #7	$98.69	5.660%	$104.2759	$104.28	$104.30	$104.30
7 purchase totals =	$1,001.27		$1,080.9525	$1,080.95	$1,080.95	$1,081.00