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	$228.62	11.696%	$255.3594	$255.36	$255.35	$255.40
Purchase #2	$196.42	3.487%	$203.2692	$203.27	$203.25	$203.30
Purchase #3	$105.32	13.292%	$119.3191	$119.32	$119.30	$119.30
Purchase #4	$242.57	7.238%	$260.1272	$260.13	$260.15	$260.10
Purchase #5	$29.52	8.682%	$32.0829	$32.08	$32.10	$32.10
Purchase #6	$166.73	11.802%	$186.4075	$186.41	$186.40	$186.40
Purchase #7	$103.96	4.452%	$108.5883	$108.59	$108.60	$108.60
7 purchase totals =	$1,073.14		$1,165.1536	$1,165.16	$1,165.15	$1,165.20