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	$73.80	11.500%	$82.287	$82.29	$82.30	$82.30
Purchase #2	$95.86	7.708%	$103.2489	$103.25	$103.25	$103.20
Purchase #3	$229.35	13.213%	$259.654	$259.65	$259.65	$259.70
Purchase #4	$139.45	3.541%	$144.3879	$144.39	$144.40	$144.40
Purchase #5	$198.27	12.208%	$222.4748	$222.47	$222.45	$222.50
Purchase #6	$78.56	10.183%	$86.5598	$86.56	$86.55	$86.60
Purchase #7	$28.82	11.596%	$32.162	$32.16	$32.15	$32.20
7 purchase totals =	$844.11		$930.7744	$930.77	$930.75	$930.90