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	$235.64	8.240%	$255.0567	$255.06	$255.05	$255.10
Purchase #2	$132.69	3.709%	$137.6115	$137.61	$137.60	$137.60
Purchase #3	$209.91	11.739%	$234.5513	$234.55	$234.55	$234.60
Purchase #4	$217.56	9.149%	$237.4646	$237.46	$237.45	$237.50
Purchase #5	$73.75	9.629%	$80.8514	$80.85	$80.85	$80.90
Purchase #6	$204.64	3.473%	$211.7471	$211.75	$211.75	$211.70
Purchase #7	$80.36	12.626%	$90.5063	$90.51	$90.50	$90.50
7 purchase totals =	$1,154.55		$1,247.7889	$1,247.79	$1,247.75	$1,247.90