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	$102.88	13.871%	$117.1505	$117.15	$117.15	$117.20
Purchase #2	$50.63	8.406%	$54.886	$54.89	$54.90	$54.90
Purchase #3	$230.32	3.813%	$239.1021	$239.10	$239.10	$239.10
Purchase #4	$95.25	7.476%	$102.3709	$102.37	$102.35	$102.40
Purchase #5	$154.46	6.567%	$164.6034	$164.60	$164.60	$164.60
Purchase #6	$70.53	11.157%	$78.399	$78.40	$78.40	$78.40
Purchase #7	$54.65	4.438%	$57.0754	$57.08	$57.10	$57.10
7 purchase totals =	$758.72		$813.5873	$813.59	$813.60	$813.70