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	$36.85	8.258%	$39.8931	$39.89	$39.90	$39.90
Purchase #2	$173.59	10.234%	$191.3552	$191.36	$191.35	$191.40
Purchase #3	$49.87	8.558%	$54.1379	$54.14	$54.15	$54.10
Purchase #4	$98.69	11.386%	$109.9268	$109.93	$109.95	$109.90
Purchase #5	$214.26	3.210%	$221.1377	$221.14	$221.15	$221.10
Purchase #6	$126.58	10.864%	$140.3317	$140.33	$140.35	$140.30
Purchase #7	$90.40	6.851%	$96.5933	$96.59	$96.60	$96.60
7 purchase totals =	$790.24		$853.3757	$853.38	$853.45	$853.30