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	$177.28	8.249%	$191.9038	$191.90	$191.90	$191.90
Purchase #2	$85.99	4.555%	$89.9068	$89.91	$89.90	$89.90
Purchase #3	$139.62	10.179%	$153.8319	$153.83	$153.85	$153.80
Purchase #4	$157.36	4.229%	$164.0148	$164.01	$164.00	$164.00
Purchase #5	$119.52	8.267%	$129.4007	$129.40	$129.40	$129.40
Purchase #6	$182.82	4.350%	$190.7727	$190.77	$190.75	$190.80
Purchase #7	$27.93	4.133%	$29.0843	$29.08	$29.10	$29.10
7 purchase totals =	$890.52		$948.9150	$948.90	$948.90	$948.90