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	$10.62	13.705%	$12.0755	$12.08	$12.10	$12.10
Purchase #2	$50.38	10.385%	$55.612	$55.61	$55.60	$55.60
Purchase #3	$245.31	8.508%	$266.181	$266.18	$266.20	$266.20
Purchase #4	$96.58	9.144%	$105.4113	$105.41	$105.40	$105.40
Purchase #5	$68.76	6.870%	$73.4838	$73.48	$73.50	$73.50
Purchase #6	$40.64	4.221%	$42.3554	$42.36	$42.35	$42.40
Purchase #7	$124.76	11.423%	$139.0113	$139.01	$139.00	$139.00
7 purchase totals =	$637.05		$694.1303	$694.13	$694.15	$694.20