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	$81.94	8.775%	$89.1302	$89.13	$89.15	$89.10
Purchase #2	$192.96	11.846%	$215.818	$215.82	$215.80	$215.80
Purchase #3	$90.53	9.406%	$99.0453	$99.05	$99.05	$99.00
Purchase #4	$152.27	7.423%	$163.573	$163.57	$163.55	$163.60
Purchase #5	$205.94	4.405%	$215.0117	$215.01	$215.00	$215.00
Purchase #6	$85.61	6.280%	$90.9863	$90.99	$91.00	$91.00
Purchase #7	$55.54	8.810%	$60.4331	$60.43	$60.45	$60.40
7 purchase totals =	$864.79		$933.9976	$934.00	$934.00	$933.90