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	$240.71	6.186%	$255.6003	$255.60	$255.60	$255.60
Purchase #2	$85.98	11.486%	$95.8557	$95.86	$95.85	$95.90
Purchase #3	$149.71	10.664%	$165.6751	$165.68	$165.70	$165.70
Purchase #4	$81.46	9.416%	$89.1303	$89.13	$89.15	$89.10
Purchase #5	$172.68	13.448%	$195.902	$195.90	$195.90	$195.90
Purchase #6	$189.80	3.439%	$196.3272	$196.33	$196.35	$196.30
Purchase #7	$103.34	13.521%	$117.3126	$117.31	$117.30	$117.30
7 purchase totals =	$1,023.68		$1,115.8032	$1,115.81	$1,115.85	$1,115.80