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	$38.48	5.293%	$40.5167	$40.52	$40.50	$40.50
Purchase #2	$178.84	7.866%	$192.9076	$192.91	$192.90	$192.90
Purchase #3	$88.48	12.424%	$99.4728	$99.47	$99.45	$99.50
Purchase #4	$78.74	12.696%	$88.7368	$88.74	$88.75	$88.70
Purchase #5	$47.26	10.374%	$52.1628	$52.16	$52.15	$52.20
Purchase #6	$236.60	9.133%	$258.2087	$258.21	$258.20	$258.20
Purchase #7	$165.38	11.155%	$183.8281	$183.83	$183.85	$183.80
7 purchase totals =	$833.78		$915.8335	$915.84	$915.80	$915.80