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	$83.90	6.309%	$89.1933	$89.19	$89.20	$89.20
Purchase #2	$244.37	10.685%	$270.4809	$270.48	$270.50	$270.50
Purchase #3	$30.48	4.411%	$31.8245	$31.82	$31.80	$31.80
Purchase #4	$87.25	9.370%	$95.4253	$95.43	$95.45	$95.40
Purchase #5	$104.92	8.401%	$113.7343	$113.73	$113.75	$113.70
Purchase #6	$139.40	12.349%	$156.6145	$156.61	$156.60	$156.60
Purchase #7	$222.84	8.798%	$242.4455	$242.45	$242.45	$242.40
7 purchase totals =	$913.16		$999.7183	$999.71	$999.75	$999.60