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	$18.25	12.488%	$20.5291	$20.53	$20.55	$20.50
Purchase #2	$210.71	4.245%	$219.6546	$219.65	$219.65	$219.70
Purchase #3	$90.40	10.221%	$99.6398	$99.64	$99.65	$99.60
Purchase #4	$83.46	3.575%	$86.4437	$86.44	$86.45	$86.40
Purchase #5	$161.70	7.548%	$173.9051	$173.91	$173.90	$173.90
Purchase #6	$147.60	12.145%	$165.526	$165.53	$165.55	$165.50
Purchase #7	$103.47	9.362%	$113.1569	$113.16	$113.15	$113.20
7 purchase totals =	$815.59		$878.8552	$878.86	$878.90	$878.80