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	$21.35	12.798%	$24.0824	$24.08	$24.10	$24.10
Purchase #2	$6.66	3.121%	$6.8679	$6.87	$6.85	$6.90
Purchase #3	$18.36	10.503%	$20.2884	$20.29	$20.30	$20.30
Purchase #4	$247.40	7.474%	$265.8907	$265.89	$265.90	$265.90
Purchase #5	$225.35	13.868%	$256.6015	$256.60	$256.60	$256.60
Purchase #6	$169.82	7.642%	$182.7976	$182.80	$182.80	$182.80
Purchase #7	$238.75	7.143%	$255.8039	$255.80	$255.80	$255.80
7 purchase totals =	$927.69		$1,012.3324	$1,012.33	$1,012.35	$1,012.40