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	$90.67	9.665%	$99.4333	$99.43	$99.45	$99.40
Purchase #2	$195.67	10.544%	$216.3014	$216.30	$216.30	$216.30
Purchase #3	$46.74	3.679%	$48.4596	$48.46	$48.45	$48.50
Purchase #4	$67.49	7.344%	$72.4465	$72.45	$72.45	$72.40
Purchase #5	$198.36	8.841%	$215.897	$215.90	$215.90	$215.90
Purchase #6	$91.27	13.757%	$103.826	$103.83	$103.85	$103.80
Purchase #7	$166.45	9.704%	$182.6023	$182.60	$182.60	$182.60
7 purchase totals =	$856.65		$938.9661	$938.97	$939.00	$938.90