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	$139.36	12.448%	$156.7075	$156.71	$156.70	$156.70
Purchase #2	$102.48	8.625%	$111.3189	$111.32	$111.30	$111.30
Purchase #3	$133.97	12.777%	$151.0873	$151.09	$151.10	$151.10
Purchase #4	$38.40	12.576%	$43.2292	$43.23	$43.25	$43.20
Purchase #5	$239.36	11.782%	$267.5614	$267.56	$267.55	$267.60
Purchase #6	$202.72	12.177%	$227.4052	$227.41	$227.40	$227.40
Purchase #7	$105.28	4.166%	$109.666	$109.67	$109.65	$109.70
7 purchase totals =	$961.57		$1,066.9755	$1,066.99	$1,066.95	$1,067.00