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	$24.43	13.356%	$27.6929	$27.69	$27.70	$27.70
Purchase #2	$203.85	4.428%	$212.8765	$212.88	$212.90	$212.90
Purchase #3	$156.37	9.592%	$171.369	$171.37	$171.35	$171.40
Purchase #4	$162.86	5.789%	$172.288	$172.29	$172.30	$172.30
Purchase #5	$162.57	7.792%	$175.2375	$175.24	$175.25	$175.20
Purchase #6	$166.45	4.722%	$174.3098	$174.31	$174.30	$174.30
Purchase #7	$90.91	12.286%	$102.0792	$102.08	$102.10	$102.10
7 purchase totals =	$967.44		$1,035.8529	$1,035.86	$1,035.90	$1,035.90