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	$242.39	13.206%	$274.4	$274.40	$274.40	$274.40
Purchase #2	$130.52	6.527%	$139.039	$139.04	$139.05	$139.00
Purchase #3	$19.61	11.301%	$21.8261	$21.83	$21.85	$21.80
Purchase #4	$245.73	11.489%	$273.9619	$273.96	$273.95	$274.00
Purchase #5	$23.59	7.852%	$25.4423	$25.44	$25.45	$25.40
Purchase #6	$228.28	8.519%	$247.7272	$247.73	$247.75	$247.70
Purchase #7	$31.60	11.795%	$35.3272	$35.33	$35.35	$35.30
7 purchase totals =	$921.72		$1,017.7237	$1,017.73	$1,017.80	$1,017.60