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	$116.54	9.818%	$127.9819	$127.98	$128.00	$128.00
Purchase #2	$123.38	3.717%	$127.966	$127.97	$127.95	$128.00
Purchase #3	$91.96	13.633%	$104.4969	$104.50	$104.50	$104.50
Purchase #4	$163.94	8.277%	$177.5093	$177.51	$177.50	$177.50
Purchase #5	$89.67	11.204%	$99.7166	$99.72	$99.70	$99.70
Purchase #6	$221.74	13.563%	$251.8146	$251.81	$251.80	$251.80
Purchase #7	$168.45	12.797%	$190.0065	$190.01	$190.00	$190.00
7 purchase totals =	$975.68		$1,079.4918	$1,079.50	$1,079.45	$1,079.50