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	$28.27	6.343%	$30.0632	$30.06	$30.05	$30.10
Purchase #2	$246.71	11.659%	$275.4739	$275.47	$275.45	$275.50
Purchase #3	$123.92	12.396%	$139.2811	$139.28	$139.30	$139.30
Purchase #4	$12.67	6.123%	$13.4458	$13.45	$13.45	$13.40
Purchase #5	$24.79	11.317%	$27.5955	$27.60	$27.60	$27.60
Purchase #6	$28.71	6.220%	$30.4958	$30.50	$30.50	$30.50
Purchase #7	$78.97	8.399%	$85.6027	$85.60	$85.60	$85.60
7 purchase totals =	$544.04		$601.9580	$601.96	$601.95	$602.00