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	$7.37	6.225%	$7.8288	$7.83	$7.85	$7.80
Purchase #2	$169.72	11.773%	$189.7011	$189.70	$189.70	$189.70
Purchase #3	$172.29	7.561%	$185.3168	$185.32	$185.30	$185.30
Purchase #4	$198.39	6.174%	$210.6386	$210.64	$210.65	$210.60
Purchase #5	$179.35	9.492%	$196.3739	$196.37	$196.35	$196.40
Purchase #6	$156.30	11.511%	$174.2917	$174.29	$174.30	$174.30
Purchase #7	$80.67	11.734%	$90.1358	$90.14	$90.15	$90.10
7 purchase totals =	$964.09		$1,054.2867	$1,054.29	$1,054.30	$1,054.20