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	$38.46	10.502%	$42.4991	$42.50	$42.50	$42.50
Purchase #2	$23.28	9.541%	$25.5011	$25.50	$25.50	$25.50
Purchase #3	$25.75	12.775%	$29.0396	$29.04	$29.05	$29.00
Purchase #4	$13.79	9.109%	$15.0461	$15.05	$15.05	$15.00
Purchase #5	$28.28	4.392%	$29.5221	$29.52	$29.50	$29.50
Purchase #6	$10.56	9.816%	$11.5966	$11.60	$11.60	$11.60
Purchase #7	$12.67	12.489%	$14.2524	$14.25	$14.25	$14.30
7 purchase totals =	$152.79		$167.4570	$167.46	$167.45	$167.40