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	$247.57	5.548%	$261.3052	$261.31	$261.30	$261.30
Purchase #2	$245.25	4.312%	$255.8252	$255.83	$255.85	$255.80
Purchase #3	$138.46	9.366%	$151.4282	$151.43	$151.45	$151.40
Purchase #4	$211.28	7.190%	$226.471	$226.47	$226.45	$226.50
Purchase #5	$165.99	3.822%	$172.3341	$172.33	$172.35	$172.30
Purchase #6	$67.96	8.620%	$73.8182	$73.82	$73.80	$73.80
Purchase #7	$151.37	11.441%	$168.6882	$168.69	$168.70	$168.70
7 purchase totals =	$1,227.88		$1,309.8701	$1,309.88	$1,309.90	$1,309.80