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	$134.33	7.361%	$144.218	$144.22	$144.20	$144.20
Purchase #2	$198.86	10.851%	$220.4383	$220.44	$220.45	$220.40
Purchase #3	$43.89	5.236%	$46.1881	$46.19	$46.20	$46.20
Purchase #4	$13.75	4.358%	$14.3492	$14.35	$14.35	$14.30
Purchase #5	$12.41	4.146%	$12.9245	$12.92	$12.90	$12.90
Purchase #6	$83.78	3.288%	$86.5347	$86.53	$86.55	$86.50
Purchase #7	$29.46	6.617%	$31.4094	$31.41	$31.40	$31.40
7 purchase totals =	$516.48		$556.0622	$556.06	$556.05	$555.90