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	$15.73	9.759%	$17.2651	$17.27	$17.25	$17.30
Purchase #2	$127.35	11.601%	$142.1239	$142.12	$142.10	$142.10
Purchase #3	$116.37	4.200%	$121.2575	$121.26	$121.25	$121.30
Purchase #4	$61.81	6.370%	$65.7473	$65.75	$65.75	$65.70
Purchase #5	$118.56	7.165%	$127.0548	$127.05	$127.05	$127.10
Purchase #6	$141.74	6.169%	$150.4839	$150.48	$150.50	$150.50
Purchase #7	$37.94	11.516%	$42.3092	$42.31	$42.30	$42.30
7 purchase totals =	$619.50		$666.2417	$666.24	$666.20	$666.30