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	$130.65	6.620%	$139.299	$139.30	$139.30	$139.30
Purchase #2	$31.27	6.377%	$33.2641	$33.26	$33.25	$33.30
Purchase #3	$156.70	8.156%	$169.4805	$169.48	$169.50	$169.50
Purchase #4	$89.54	11.198%	$99.5667	$99.57	$99.55	$99.60
Purchase #5	$215.42	10.286%	$237.5781	$237.58	$237.60	$237.60
Purchase #6	$38.91	11.777%	$43.4924	$43.49	$43.50	$43.50
Purchase #7	$214.67	7.635%	$231.0601	$231.06	$231.05	$231.10
7 purchase totals =	$877.16		$953.7409	$953.74	$953.75	$953.90