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	$237.91	13.858%	$270.8796	$270.88	$270.90	$270.90
Purchase #2	$21.55	9.506%	$23.5985	$23.60	$23.60	$23.60
Purchase #3	$17.61	3.869%	$18.2913	$18.29	$18.30	$18.30
Purchase #4	$102.82	6.699%	$109.7079	$109.71	$109.70	$109.70
Purchase #5	$148.94	13.832%	$169.5414	$169.54	$169.55	$169.50
Purchase #6	$189.80	13.541%	$215.5008	$215.50	$215.50	$215.50
Purchase #7	$106.72	4.720%	$111.7572	$111.76	$111.75	$111.80
7 purchase totals =	$825.35		$919.2767	$919.28	$919.30	$919.30