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	$178.69	6.176%	$189.7259	$189.73	$189.75	$189.70
Purchase #2	$120.57	8.756%	$131.1271	$131.13	$131.15	$131.10
Purchase #3	$184.85	6.721%	$197.2738	$197.27	$197.25	$197.30
Purchase #4	$125.58	4.601%	$131.3579	$131.36	$131.35	$131.40
Purchase #5	$169.46	7.715%	$182.5338	$182.53	$182.55	$182.50
Purchase #6	$241.59	8.579%	$262.316	$262.32	$262.30	$262.30
Purchase #7	$101.86	9.782%	$111.8239	$111.82	$111.80	$111.80
7 purchase totals =	$1,122.60		$1,206.1584	$1,206.16	$1,206.15	$1,206.10