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	$229.82	8.846%	$250.1499	$250.15	$250.15	$250.10
Purchase #2	$74.31	8.637%	$80.7282	$80.73	$80.75	$80.70
Purchase #3	$94.42	13.495%	$107.162	$107.16	$107.15	$107.20
Purchase #4	$226.69	12.542%	$255.1215	$255.12	$255.10	$255.10
Purchase #5	$41.88	12.618%	$47.1644	$47.16	$47.15	$47.20
Purchase #6	$198.53	9.231%	$216.8563	$216.86	$216.85	$216.90
Purchase #7	$125.50	12.457%	$141.1335	$141.13	$141.15	$141.10
7 purchase totals =	$991.15		$1,098.3158	$1,098.31	$1,098.30	$1,098.30