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	$52.60	4.130%	$54.7724	$54.77	$54.75	$54.80
Purchase #2	$150.40	12.549%	$169.2737	$169.27	$169.25	$169.30
Purchase #3	$216.37	11.847%	$242.0034	$242.00	$242.00	$242.00
Purchase #4	$201.71	11.803%	$225.5178	$225.52	$225.50	$225.50
Purchase #5	$155.79	6.269%	$165.5565	$165.56	$165.55	$165.60
Purchase #6	$232.46	11.758%	$259.7926	$259.79	$259.80	$259.80
Purchase #7	$114.34	10.651%	$126.5184	$126.52	$126.50	$126.50
7 purchase totals =	$1,123.67		$1,243.4348	$1,243.43	$1,243.35	$1,243.50