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	$36.84	8.651%	$40.027	$40.03	$40.05	$40.00
Purchase #2	$99.63	10.162%	$109.7544	$109.75	$109.75	$109.80
Purchase #3	$67.55	4.241%	$70.4148	$70.41	$70.40	$70.40
Purchase #4	$133.50	12.438%	$150.1047	$150.10	$150.10	$150.10
Purchase #5	$165.90	11.852%	$185.5625	$185.56	$185.55	$185.60
Purchase #6	$196.81	12.355%	$221.1259	$221.13	$221.15	$221.10
Purchase #7	$167.83	9.287%	$183.4164	$183.42	$183.40	$183.40
7 purchase totals =	$868.06		$960.4057	$960.40	$960.40	$960.40