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	$249.38	3.147%	$257.228	$257.23	$257.25	$257.20
Purchase #2	$160.30	7.203%	$171.8464	$171.85	$171.85	$171.80
Purchase #3	$68.90	4.572%	$72.0501	$72.05	$72.05	$72.10
Purchase #4	$30.83	8.339%	$33.4009	$33.40	$33.40	$33.40
Purchase #5	$187.88	12.518%	$211.3988	$211.40	$211.40	$211.40
Purchase #6	$153.51	10.655%	$169.8665	$169.87	$169.85	$169.90
Purchase #7	$163.84	13.132%	$185.3555	$185.36	$185.35	$185.40
7 purchase totals =	$1,014.64		$1,101.1462	$1,101.16	$1,101.15	$1,101.20