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	$49.91	11.872%	$55.8353	$55.84	$55.85	$55.80
Purchase #2	$133.70	7.413%	$143.6112	$143.61	$143.60	$143.60
Purchase #3	$225.98	6.806%	$241.3602	$241.36	$241.35	$241.40
Purchase #4	$156.82	3.460%	$162.246	$162.25	$162.25	$162.20
Purchase #5	$190.72	4.278%	$198.879	$198.88	$198.90	$198.90
Purchase #6	$218.32	12.485%	$245.5773	$245.58	$245.60	$245.60
Purchase #7	$91.65	12.352%	$102.9706	$102.97	$102.95	$103.00
7 purchase totals =	$1,067.10		$1,150.4796	$1,150.49	$1,150.50	$1,150.50