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	$91.52	13.851%	$104.1964	$104.20	$104.20	$104.20
Purchase #2	$25.96	10.199%	$28.6077	$28.61	$28.60	$28.60
Purchase #3	$128.94	10.149%	$142.0261	$142.03	$142.05	$142.00
Purchase #4	$189.89	10.288%	$209.4259	$209.43	$209.45	$209.40
Purchase #5	$52.26	9.701%	$57.3297	$57.33	$57.35	$57.30
Purchase #6	$12.73	8.142%	$13.7665	$13.77	$13.75	$13.80
Purchase #7	$18.73	8.665%	$20.353	$20.35	$20.35	$20.40
7 purchase totals =	$520.03		$575.7053	$575.72	$575.75	$575.70