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	$52.25	12.766%	$58.9202	$58.92	$58.90	$58.90
Purchase #2	$101.41	8.160%	$109.6851	$109.69	$109.70	$109.70
Purchase #3	$54.79	9.324%	$59.8986	$59.90	$59.90	$59.90
Purchase #4	$105.46	9.738%	$115.7297	$115.73	$115.75	$115.70
Purchase #5	$77.77	5.266%	$81.8654	$81.87	$81.85	$81.90
Purchase #6	$112.69	5.393%	$118.7674	$118.77	$118.75	$118.80
Purchase #7	$96.32	6.551%	$102.6299	$102.63	$102.65	$102.60
7 purchase totals =	$600.69		$647.4963	$647.51	$647.50	$647.50