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	$88.61	12.861%	$100.0061	$100.01	$100.00	$100.00
Purchase #2	$94.85	4.765%	$99.3696	$99.37	$99.35	$99.40
Purchase #3	$153.27	5.324%	$161.4301	$161.43	$161.45	$161.40
Purchase #4	$149.67	13.515%	$169.8979	$169.90	$169.90	$169.90
Purchase #5	$60.90	4.214%	$63.4663	$63.47	$63.45	$63.50
Purchase #6	$103.26	6.307%	$109.7726	$109.77	$109.75	$109.80
Purchase #7	$201.30	8.520%	$218.4508	$218.45	$218.45	$218.50
7 purchase totals =	$851.86		$922.3934	$922.40	$922.35	$922.50