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	$80.43	11.826%	$89.9417	$89.94	$89.95	$89.90
Purchase #2	$203.96	6.127%	$216.4566	$216.46	$216.45	$216.50
Purchase #3	$74.60	3.666%	$77.3348	$77.33	$77.35	$77.30
Purchase #4	$203.93	11.394%	$227.1658	$227.17	$227.15	$227.20
Purchase #5	$31.40	3.347%	$32.451	$32.45	$32.45	$32.50
Purchase #6	$24.29	13.215%	$27.4999	$27.50	$27.50	$27.50
Purchase #7	$128.72	5.150%	$135.3491	$135.35	$135.35	$135.30
7 purchase totals =	$747.33		$806.1989	$806.20	$806.20	$806.20