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	$20.85	12.606%	$23.4784	$23.48	$23.50	$23.50
Purchase #2	$230.28	13.413%	$261.1675	$261.17	$261.15	$261.20
Purchase #3	$36.40	7.404%	$39.0951	$39.10	$39.10	$39.10
Purchase #4	$106.27	12.776%	$119.8471	$119.85	$119.85	$119.80
Purchase #5	$39.95	13.409%	$45.3069	$45.31	$45.30	$45.30
Purchase #6	$113.91	4.383%	$118.9027	$118.90	$118.90	$118.90
Purchase #7	$84.42	7.447%	$90.7068	$90.71	$90.70	$90.70
7 purchase totals =	$632.08		$698.5045	$698.52	$698.50	$698.50