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	$53.76	8.745%	$58.4613	$58.46	$58.45	$58.50
Purchase #2	$216.60	13.837%	$246.5709	$246.57	$246.55	$246.60
Purchase #3	$114.40	11.270%	$127.2929	$127.29	$127.30	$127.30
Purchase #4	$245.56	12.312%	$275.7933	$275.79	$275.80	$275.80
Purchase #5	$18.83	9.425%	$20.6047	$20.60	$20.60	$20.60
Purchase #6	$13.38	9.195%	$14.6103	$14.61	$14.60	$14.60
Purchase #7	$197.48	12.445%	$222.0564	$222.06	$222.05	$222.10
7 purchase totals =	$860.01		$965.3898	$965.38	$965.35	$965.50