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	$89.26	11.471%	$99.499	$99.50	$99.50	$99.50
Purchase #2	$145.57	12.737%	$164.1113	$164.11	$164.10	$164.10
Purchase #3	$24.57	11.458%	$27.3852	$27.39	$27.40	$27.40
Purchase #4	$77.73	9.804%	$85.3506	$85.35	$85.35	$85.40
Purchase #5	$134.31	4.773%	$140.7206	$140.72	$140.70	$140.70
Purchase #6	$26.55	7.726%	$28.6013	$28.60	$28.60	$28.60
Purchase #7	$50.54	5.716%	$53.4289	$53.43	$53.45	$53.40
7 purchase totals =	$548.53		$599.0969	$599.10	$599.10	$599.10