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	$123.83	12.673%	$139.523	$139.52	$139.50	$139.50
Purchase #2	$85.99	5.445%	$90.6722	$90.67	$90.65	$90.70
Purchase #3	$51.89	6.289%	$55.1534	$55.15	$55.15	$55.20
Purchase #4	$115.74	6.436%	$123.189	$123.19	$123.20	$123.20
Purchase #5	$150.99	7.129%	$161.7541	$161.75	$161.75	$161.80
Purchase #6	$159.25	8.563%	$172.8866	$172.89	$172.90	$172.90
Purchase #7	$244.62	3.741%	$253.7712	$253.77	$253.75	$253.80
7 purchase totals =	$932.31		$996.9495	$996.94	$996.90	$997.10